Taxation in the Greco-Roman World: The Roman Principate

τό τε σύμπαν εἰπεῖν, χρηματοποιὸς ἀνὴρ ἐγένετο, δύο τε εἶναι λέγων τὰ τὰς δυναστείας παρασκευάζοντα καὶ φυλάσσοντα καὶ ἐπαύξοντα, στρατιώτας καὶ χρήματα, καὶ ταῦτα δι᾽ ἀλλήλων συνεστηκέναι: τῇ τε γὰρ τροφῇ τὰ στρατεύματα συνέχεσθαι, καὶ ἐκείνην ἐκ τῶν ὅπλων συλλέγεσθαι: κἂν θάτερον ὁποτερονοῦν αὐτῶν ἐνδεὲς ᾖ, καὶ τὸ ἕτερον συγκαταλυθήσεσθαι.

“In short, he [sc. Caesar] showed himself a money-getter, declaring that there were two things which created, protected, and increased sovereignties,—soldiers and money,—and that these two were dependent upon each other. For it was by proper maintenance, he said, that armies were kept together, and this maintenance was secured by arms; and in case either one of them were lacking, the other also would be overthrown at the same time.” (D.C. 42.49.4sq., transl. E. Cary, 1916, Dio’s Roman History, Vol. 4 [LCL], London and New York.)

This almost prophetic sentence of C. Julius Caesar in 47 bc after the battle of Zela against Pharnaces II and the (financial) measures undertaken by him in the east is perhaps not as famous as his “veni, vidi, vici” but may be more striking when one looks at the fundamentals of the future Principate. In fact, it was the troops in the imperial provinces as well as the funds of the fiscus Caesaris that allowed the princeps Augustus to establish and keep control over the res publica (restituta)—besides his outstanding auctoritas (Monum. Ancyr. 34.3) and the other official potestates. This was also true for his successors, for which reason studies on military power as well as on financial potential are essential to reveal the origin and status of the Roman emperor and his principate.

There is still an imbalance between the rich amount of research done in the military field and the rather scattered studies on the financial sector. This is primarily due to the lack of broad evidence, which causes a fragmentation into several research fields that cannot be easily combined, especially in the field of Roman taxation, where the exiguous literary evidence has to be compared with epigraphical, papyrological, and numismatic sources using the full range of methods of analysis. This contribution, therefore, tries to show some possible approaches to a study of Roman taxes and to add them as one of the more important tesserae to the mosaic of the Roman Empire.

Every study of (Greek and) Roman taxation has, at first, to deal with terminology (cf. Günther 2008: 14–21). In fact, Roman terminology, deriving from the Roman Republic, is quite clear. For example, tributa / stipendia are distinguished from vectigalia and in most cases portoria, especially tributa from vectigalia. So Tacitus (Tac. Ann. 1.11.3 sq.; cf. Suet. Aug. 101.4) differentiates clearly between the two in Augustus’ report after his death in 14 ad, brought and read to the senate by order of Tiberius: … cum proferri libellum recitarique iussit. Opes publicae continebantur, quantum civium sociorumque in armis, quot classes regna provinciae, tributa aut vectigalia, et necessitates ac largitiones “ … when he ordered a booklet to be produced and read out. Its contents were the public resources, what numbers of citizens and allies under arms, how many fleets, kingdoms and provinces, taxes and revenues, and also necessary expenses and lavishments” (transl. A. J. Woodman, 2004, Tacitus, The Annals, Indianapolis and Cambridge).

By tributa / stipendia are always meant taxes raised on the basis of a census or tax list. Because of their exclusive status (this is largely true for all citizens of a state in antiquity), these tributa were not levied on Roman citizens, but only in exceptional circumstances, as in war. After 167 bc, there were no longer such tributa (Plin. HN 33.56), only in rare emergency situations (cf. esp. Nicolet 1976; Wolters 2007: 410–412, with further literature). The term was finally transferred to describe the status of the inhabitants of the provinces, who were liable, for example, to a tributum capitis (poll tax) or tributum soli (land tax), calculated on basis of a (census) list. In most cases, the Romans tied the tax levy to the tradition of the territory and the former regime. The term stipendium / provincia stipendiaria was also common to show that the territory had been acquired by a Roman conquest with a military guerdon (stipendium) to be paid by the inhabitants.

In contrast, vectigal, etymologically deriving from vehere (to convey or transport), first designated the cartloads of crops from ager publicus (public land) that had to be given to the state as landlord by the leaseholder. As a consequence, only the ratio could be defined in advance, but not the exact amount, which depended on the harvest, and this concept later defined also the taxes called vectigalia: they were not raised on the basis of (census) lists but on occasion. In this framework, the portoria (customs) were not a special case, so vectigalia and portoria were often interchangeable terms, as in the definition in the Digests of Justinian, deriving from the jurist Ulpian (Dig. 50.16.17.1): “Publica” vectigalia intellegere debemus, ex quibus vectigal fiscus capit: quale est vectigal portus vel venalium rerum, item salinarum et metallorum et picariarum “We have to understand public taxes as those from which the Treasury captures revenue: for instance, the tax of the harbor or the tax on selling products, likewise on salt-pits and mines and bitumen-fabrics” (transl. Günther 2015).

However, the distinction is not kept up in every source. Sometimes vectigal is used to describe tributa or stipendia as a generic term. The use can often be linked to the intentions of the ancient authors, for instance to undermine the authority of an emperor. Thus, Suetonius describes the tax levied by the “bad” ruler Caligula (37–41 ad) by mixing vectigalia, which were possible and even common for Roman citizens, with the term tributum, calling this an outrageous and improper measure for the status of Roman citizenship (Suet. Calig. 40): Vectigalia nova atque inaudita primum per publicanos, deinde, quia lucrum exuberabat, per centuriones tribunosque praetorianos exercuit, nullo rerum aut hominum genere omisso, cui non tributi aliquid imponeret “He levied new [so-called indirect] taxes, and such as were never before known, at first by the publicans, but afterwards, because their profit was enormous, by centurions and tribunes of the pretorian guards; no description of property or persons was exempted from some kind of [so-called direct] tax” (transl. J. Eugene Reed and Alexander Thomson, 1889, Suetonius: The Lives of the Twelve Caesars, Philadelphia).

What is crucial is how to translate tributum and vectigal. Until the twentieth century, tributum was translated by “direct tax” and vectigal by “indirect tax,” in an attempt at adequate differentiation. But this does not fit modern economic tax theory, notably the idea that indirect taxes, such as purchase tax, can be turned over to third parties. Therefore, some researchers tend to consider nearly all vectigalia (except the tax on sales) direct taxes in this sense, because they had to be paid directly by the person liable to the tax (e.g. Eck 1979: 132 no. 92; Neesen 1980: 200s no. 18,5). But this is not the concept of (Roman) antiquity, where the classification of tributa or vectigalia depended on the tax being levied with or without a (census) list. Therefore a better translation nowadays would be “so-called direct tax” for tributum and “so-called indirect tax” for vectigal.

With the end of tributa on Roman citizens in 167 bc—with some exceptions in times of crises during the Late Roman Republic—the term was increasingly used for describing the tribute status of the Roman provinces, interchangeably with the term stipendium, depending on author and view (see above). A main characteristic of Roman rule in the provinces was letting traditional systems continue as long as they worked and were adaptable to Roman necessities. It is no wonder that alongside tributum and stipendium terms like decuma (pars) “the tenth (part)” were used to describe the tributes of provincial inhabitants according to the traditional rate.

In the Republic and Principate, the main tributa were the tributum soli (land tax) and the tributum capitis (poll tax) (cf. the essential study Neesen 1980; discussion and corrections in Brunt 1981 / 1990). Like all tributa, they were calculated on the basis of a census list. Details concerning the measurement are unclear, due to the various and fragmentary evidence; what is clear is that there were different treatments of provincial lands: besides the “normal” provincial land liable to the tributum soli there were also privileges for Roman colonies (ager privatus ex iure Quiritium “private land according to Roman right”) or civitates foederatae (confederated commonwealths) or civitates liberae (free commonwealths), with certain immunitates (immunities). But what had to be declared besides the land is not entirely clear (cf. the discussion in Brunt 1981 / 1990: 166–168 / 335–339), for example property except land or moveables (under the tributum capitis?). This is true for the tributum capitis, which had different rates in the various provinces (cf. for explanations Neesen 1980: 120 sqq.; Brunt 1981 / 1990: 167 sq. / 338 sq.).

These important questions—whether one is discussing a systematization of Roman taxation or only situational changes—cannot be solved, because of the diverse evidence from the provinces. The main evidence comes from Egypt. For a long time, it was treated as a special case because of its different status in the administration structure of the Roman Empire (Wallace 1938; Neesen 1980; Brunt 1981 / 1990). But in recent research there is considerable discussion on this issue, and Egypt is now often seen as a normal case in the Empire, with certain peculiarities as in other provinces (clearly against such a special role of Egypt: Jördens 2009, esp. for customs chap. I–IX; Jördens 2012; for customs, see also Vandorpe 2015; cautious: Eich 2007). Studies of other provinces analyzing systematically the material and new findings could perhaps reveal more details (cf. for Gallic and German provinces France 2001b; for Iudaea, Udoh 2005).

Smaller tributa as well as other dues (e.g., aurum coronarium “gold wreaths, crowns”) are treated in Neesen (1980). Greater attention has been devoted to the fiscus Iudaicus (Jewish treasury), which was the treasury for the τιμὴ δηναρίων δύο Ἰουδαίων (tax of two denarii of the Jews) exacted from the Jews after the Roman-Jewish War of 66–70 ad (cf. Günther 2013 with further literature).

All these tributa (and the other dues) were at first collected by publicans in Republican times. The change to direct collection by state officials can be attributed to Caesar (cf. the broad discussion in Brunt 1990: esp. 355 sq., 380 sq.).

Several studies have been devoted to the question of tax flow into the different treasuries of the Roman Principate (cf. Alpers 1995 with older literature; his model is modified by Wolters 1999; 174–202; Wolters 2007: 422–424; for the administration offices, cf. now Schmall 2011). It now seems clear that there were provincial fisci which balanced their yearly accounts either with the aerarium Saturni (treasury of Saturn), in the case of senatorial provinces, or with the fiscus Caesaris (treasury of the Emperor), in the case of imperial provinces. This fiscus Caesaris can probably be distinguished from the patrimonium Caesaris (patrimony of the Emperor), and later the res privata (private treasure) of certain emperors, when the patrimonium also became public. Here the main problem lies in the intention of many authors to create a “good” or “bad” emperor. But tributa (as well as the other taxes and duties) had to be paid to both, so the effect on and interest for “normal” citizens of this subtlety was, perhaps, limited.

Vectigalia in its proper sense (without portoria, see below) can be divided into empire-wide vectigalia, to which all Roman citizens were liable, and local vectigalia, for citizens of city-states in the Roman East, among others. While the latter have not been systematically studied (cf. Il capitolo delle entrate nelle finanze municipali in occidente ed in oriente 2009), the vectigalia for Roman citizens have been the object of research since the Renaissance, especially during the nineteenth and at the beginning of the twentieth century in Germany and France (for an overview, cf. Günther 2008: 8–14). These studies did not arise solely out of antiquarian interest; the scholars also wanted to compare the Roman tax system with their own, established as a consequence of the formation of nations and the rise of nationalism, which searched for roots in history. Hence studies like those of J. J. Bachofen (1848), M. R. Cagnat (1966 [1882]), or G. Schanz (1900) not only collected the scattered material (in ancient literature and law, inscriptions, papyri, numismatics) but tried to develop a systematic structure of taxation as well. On this basis, further research could be done concerning special questions like tax collectors, state treasuries, imperial administration, and the budget—questions which were important for research mainly concentrating on the state as an entity. G. Wesener´s articles concerning the vicesima hereditatium and vicesima libertatis in the RE (1958) were fundamental for further studies in this field. With the emergence of new paradigms in research, especially after World War II, special studies on the social, socioeconomic, and legal connections of vectigalia followed (cf. Günther 2008: 8–14). In his PhD thesis, the present author tried to show the synergisms between the different vectigalia and imperial policy, administration, society, and law (Günther 2008).

Of the four important and long-lived vectigalia, the most prominent (and studied) is the vicesima hereditatium, a 5 percent tax on inheritances and legacies (cf. Günther 2008: 23–94). Although some scholars have claimed that the inheritance tax was introduced with the lex Voconia 169 bc, this is certainly not true. Also, Julius Caesar had only a vague, if any, plan for a tax on heritages. A first, but short-lived, tribute on heritages and legacies in 40 bc (App. BC 5.67.282; cf. D.C. 55.25.6) during the Civil Wars after the death of Caesar was intended to finance the war against Sextus Pompeius as well as to disturb the old aristocratic networks (see Günther 2015a). The lex Falcidia, often regarded as a subsidiary measure, was enacted not in that year but in the previous year (D.C. 48.33.4 sq.), so that such a connection is not possible. But from the failure of this measure (App. BC 5.130.540), Augustus could later draw lessons for his establishment of the vicesima hereditatium in 6 ad.

Thus, the main purpose of Augustus’ introduction of the inheritance tax was not, as often suggested, an equalization of burdens between provincial inhabitants, who were not liable to vectigal but to tributa, and Roman citizens, but to provide security for his rule. A main factor for this security was the loyalty of the army, and among the measures that led to a professional standing army the possibly dangerous veterans could not be forgotten, as shown by the allotment of land to them in the first century bc, especially during the Civil Wars (cf., e.g., Monum. Ancyr. 3.3). Therefore Augustus erected the aerarium militare (military treasury [for veterans]) in 5 ad (for the history of this treasury, see Corbier 1974) to pay praemia militiae (veteran soldiers’ bonus) to his veterans instead of having to confiscate land as a reward for them. A main source of revenue for this new treasury, besides the centesima rerum venalium (see below) and some deposits from the patrimony of Augustus as well as from other private persons, was the vicesima hereditatium established shortly afterward. Resistance to this new vectigal from the rich classes (senatorial and equestrian orders) most liable to it in 6 and 13 ad was cleverly broken by Augustus by threatening the aristocracy with reinstitution of the tributum soli (land tax), which would have been the first permanent one since 167 bc.

The regulatory framework of the inheritance tax was laid down in the lex <Iulia de> vicesima hereditatium. In the main, it aimed to improve the flow of revenue into the aerarium militare. Regulations concerning the opening of a testament accelerated the enforcement of the last will of the decedent, and the payment of the tax as well; the requirement to open the testament before an official, the short deadlines for the opening of the last will, and the decentralization of the administration offices promised legal certainty for the heirs, especially in terms of possible legal cases. However, the procedure had the main purpose of recording these wills for the tax-collectors present in the bureaus. So the traditional possibility of private testaments as well as of inheritance without a written will would be gradually ended.

In the same way, the exemption for small heritages [perhaps up to 1,000 sestertii (HS)] was a beneficence of the emperor to “normal” citizens only secondarily; the estimation of the transaction costs for measuring the tax for these wills was probably the primary reason for the exemption. The second exemption, for second-degree relatives, was not only a matter of cost but also served the purposes of quieting resistance as well as strengthening the traditional family, in accordance with Augustan family laws, and inhibiting the traditional networking in the upper classes through inheritances and legacies (see Günther 2015a).

Later modifications of the Augustan lex were mainly caused by the change of conditions in the Roman Empire. Most prominent are the reforms undertaken by the emperors Nerva (96–98 ad) and Trajan (98–117 ad) to include new citizens in the regulation framework. Although they were also granted tax exemption, the assurance of revenue was the background of these measures, especially the registration of huge inheritances and the avoidance of high administration costs for difficult legal cases.

For the latter, the Roman state at first leased the collection of this vectigal (and others as well) to private companies (for their structure see Cimma 1981; Malmendier 2002; esp. concerning taxes: Brunt 1990). As with the inheritance tax, we have evidence for it in Trajanic times (through Pliny the Younger) as well as from Egypt in papyri under the reign of Antoninus Pius (138–160 ad) (cf. Eck 1995). Although there has been considerable discussion on the status of Egypt as a special case in the Roman Empire (see above), both types of evidence disprove the old opinion that there was a direct replacement of the private collectors by public procuratores XX hereditatium or a three-step process from private companies to single tax collectors and then to public officials (Günther 2008: esp. 59–69, see also the discussion for the portoria, below). Even though a precise date cannot be found in existing sources, it is likely that there is a connection between the establishment of these administrative boards and the broad reforms under the emperor Nero (54–68 ad) to control the publicans more strictly in 58 ad (see Rathbone 2008; Günther 2013). But if, when, and how these procuratores undertook the tax collection instead of private tax farmers remains an open question. It was a more gradual and situation-specific process that led to a tax collection by imperial officials instead of private persons (or sometimes together with them? AE 1996: 1702; cf. Günther 2008: 68 sq.; see also below for the portoria).

Concerning these officials, we have a rather broad range of evidence which allows us to reconstruct the administrative structure. In all places where a substantial number of Roman citizens lived, as in Rome, Italy, and in some provinces (especially the Spanish and Gaulish ones), we find a carefully built administration (cf. Günther 2008: 69–81; esp. also Eck 1979: 132–139; esp. for the equestrian procuratores: Pflaum 1960; 1982; for imperial freedmen and slaves: Wachtel 1966; see now Schmall 2011 for the finance administration staff). At the top there were procuratores XX hereditatium. Procurators outside of the equestrian order existed immediately before the reign of emperor Hadrian (117–138 ad), who was formerly thought to have replaced freedmen as officials with them, so it is more probable that there was a hierarchical structure from equestrians down to imperial freedmen and then to imperial slaves. Under these procuratores we have supprocuratores and an extensive staff, especially for the administration in Rome, where the Roman senators had their patria and all revenues of the inheritance tax may have been registered. For provinces with a smaller percentage of Roman citizens, larger administration districts were built, for example in Asia Minor. According to the distribution of possible subjects of the tax, the salaries for the procurators were measured as well: procurators for certain regions or districts earned 60,000 HS, while the procurator for Rome received 100,000 HS, or at most 200,000 HS.

The eldest vectigal was the vicesima libertatis vel manumissionum, a 5 percent tax payable when manumitting a slave to become a libertus/liberta according to Roman law (cf. Günther 2008: 95–126; also Bradley 1984; Albana 1987). Established in 357 bc (Liv. 7.16.7sq.), it probably lasted as the vicesima hereditatium up to reforms of Diocletian, and the revenues went into the aerarium Saturni populi Romani, and in Republican times into a special reserve fund, the aerarium sanctius. The fiscus libertatis et peculiorum (treasury of liberty and separate property) in the Roman Empire (with evidence from Claudian times on), which some have suggested was the fund of the tax on manumissions, was probably a special fund for imperial slaves and freedmen (Günther 2008: 101 sq.). Although the concrete reasons for establishing the tax are not entirely clear—financial need or a patrician measure against the plebeians—an increase of revenue due to the inflow of slaves in the third and second centuries bc (and, therefore, more manumissions) is likely.

Two factors led to an increase of tax revenue in the Roman Empire even though there was no great increase in the number of new slaves. On the one hand, the different legal regulations concerning manumission (e.g. Gai. Inst. 1.16–24; cf. Günther 2008: 118–120) “forced” the manumittor to undertake this act in public before a Roman magistrate to gain Roman citizenship for his freedman instead of the debased ius Latinum Iunianum. This requirement was even increased by the Augustan legislation concerning the manumitting of slaves (lex Aelia Sentia, lex Fufia Caninia, lex Iunia Norbana); with this public process, registration and tax collection were easy for the leaseholders (or, later on, the public tax officials). On the other hand, the slaves’ owners were geared to economic interests: not only the motivation of slaves to receive the status of freedman, which caused a gain of efficiency that compensated for the purchase price, but also the tradition that most slaves bought their freedom while paying the manumitting fees and taxes with their peculium (separate property) were strong push-factors. Furthermore, the new freedmen were in legal, social, and economic ways closely connected to the former owners and their families through the patron-client relationship, so that the profits for the manumitting family continued over more than one generation.

The vicesima libertatis vel manumissionum (5 percent tax on liberty or manumissions) was also exacted by private tax collectors, who interacted with a gradually growing number of public officials. Except for the vicesima hereditatium, we have insights into the world of the private tax farmer due to literary notices, inscriptions, and papyrological evidence. Not only single persons related to one or another hierarchical level but also societates publicanorum (companies of publicans) are attested in inscriptions. However, neither the reconstruction of regional tax districts nor the distribution of duties, nor a diachronic development of both, is possible due to the limits of evidence (differently from the public officials for the inheritance tax).

As for the inheritance tax, former hypotheses of a change from societates publicanorum to single tax collectors cannot be substantiated, nor can the idea that public officials replaced the private tax collection process immediately after the institution of the new tax. Private tax collectors are mentioned up to Hadrianic times, possibly up to the third century ad (AE 2001: 1707; cf. Günther 2008: 109 sq.). As for other vectigalia, the Neronian reforms of 58 ad might have established the procuratores XX libertatis to control the publicani instead of the magistrates of the aerarium populi Romani. With the first attested procurator XX libertatis in Pompeii before the eruption of Vesuvius, the hypothesis of a development from freedman to equestrian procurators also fails. Details about this sexagenary office, involving the staff or the regional administration, are difficult to estimate in the absence of evidence, but a parallel development to the (higher-paid) procurators for the vicesima hereditatium seems likely.

The details of the taxing process, as well as of the cooperation between private tax collectors and public officials, were laid down in a lex, but the concrete regulations are unknown. Thanks to papyri from Roman Egypt, we can deduce some details. In case of public manumissions as well as testamentary releases, the public administration gave notice to the tax collectors; based on a measure of value of the slave, the tax was calculated and had to be paid directly. In case of greater numbers of manumissions, for example as a result of a testament, there could also be an agreement about a flat rate. How the measurement was made is unclear. Documents concerning the purchase price or the sum paid by the slave for manumission or the current market price may have been the basis. Possibly, the attested combined lease of the vicesima liberatis together with the sale tax on slaves (quinta et vicesima venalium mancipiorum, ILS 203 = CIL VI 915, see below) was also an efficient instrument for the core of the tax collecting process. That the reduction of transaction costs, to speak in the terms of New Institutional Economics, and the increase of efficient tax collection were not unknown to the Romans is also clearly shown by the tax collecting station for both taxes, the statio vicesimae hereditatium et manumissionum (collection station for the 5 percent tax on inheritances and manumissions), in Egypt (cf. Eck 1995) and the probable lease and administration of four vectigalia under the name quattuor publica Africae (four public [taxes] for Africa) (cf. Günther 2008: e.g. 63 sq.).

The centesima rerum venalium and the quinta et vicesima venalium mancipiorum formed the so-called sales taxes but were probably not closely connected with each other.

The 1 percent sales tax (centesima rerum venalium) was established at an unknown date after the Civil Wars between Octavian and Marc Antony (Tac. Ann. 1.78.2) (see Günther 2008: 127–147). All proposals for an exact date fail due to the attempt to connect the tax with other events, which provides an insight into the mindset of modern scholars. It is a fact that under the reign of Tiberius (14–37 ad) the tax was a factor in financing the aerarium militare; therefore, Tiberius refused to abolish it in 15 ad (Tac. Ann. 1.78.2). In 17 ad, after the creation of the province Cappadocia, the tax was reduced to 0.5 percent (Tac. Ann. 2.42.4). Later on, in 31 ad, Cassius Dio tells us that the tax was exacted again at 1 percent (D.C. 58.16.2). Under the reign of Caligula, the tax, now again under the denomination of a ducentesima (0.5 percent), was cancelled in 38 ad (Suet. Calig. 16.3; cf. also D.C. 59.9.6, who writes in Greek about the centesima). This event was also celebrated propagandistically with the issue of coins, namely quadrantes (RIC I²  Caligula 111 [Nr. 39, 45, 52]; cf. Wolters 2005: 511 sq.). Because these quadrantes circulated mainly in Italy, one has to doubt older paradigms that the sales tax had a long afterlife, for example in the merces (charge) of the receipt tablet of L. Caecilius Iucundus in Pompeii in the 50s (CIL IV 3340 tab. X; tab. LVIII) or as the centesima argentariae stipulationis (1 percent on bank stipulations) in the lex metalli Vipascensis (FIRA I² no. 105, ll. 1–9) from the middle of the second century ad. In fact, the tax was exacted at public sales auctions, the only way for tax collectors to control either seller or purchaser efficiently. But both, merces and centesima, were more probably charges or the lease of exacting charges than what we would call a sales tax (Günther 2008: 134–140). There is also no direct connection with other customs duties on sales in later times (Günther 2008: 146 sq.; see now Wojciech 2015).

The 4 percent tax on the sale of slaves (quinta et vicesima venalium mancipiorum) was established in 7 ad (D.C. 55.31.4) to finance the campaign in Pannonia as well as the newly arranged cohortes vigilum (fire service cohorts) (cf. Günther 2008: 149–154). At first, the tax was, according to the Greek term τὸ τέλος τὸ τῆς πεντηκοστῆς in Cassius Dio (see above), a 2 percent tax, but at an unknown date before Claudian times (ILS 203 = CIL VI 915), the rate was changed to 4 percent. The revenues flowed into the aerarium Saturni, for which reason the tax is called a publicum vectigal (ILS 203 = CIL VI 915; CIL XV 7255). Under Nero, in 57 ad, there was a change in the charging process (Tac. Ann. 13.31.2): henceforth, the seller of slaves rather than the purchaser had to pay the tax, making it easier to control. Nothing is known about the further development of the tax; perhaps it was part of the quattuor publica Africae, and it was probably collected up to the third century ad.

Connections and analogies with the centesima rerum venalium have often been proposed but cannot be proved, due to the lack of evidence. Instead, the tax was exacted by private tax collector companies (CIL XV 7255 and the following), together with the manumission tax (ILS 203 = CIL VI 915), which also went into the aerarium Saturni rather than the aerarium militare, unlike the centesima rerum venalium. Thus it is more likely that the manumission tax and the sales tax on slaves were (sometimes? often?) leased together for efficient collection.

There has also been discussion of the minor and usually only temporarily levied vectigalia (cf. Günther 2008: 155–161), the measures of the emperor Gaius (Caligula) and the proverbial “urine tax” (pecunia non olet “money does not stink,” deriving from Suet. Vesp. 23.3; cf. D.C. 66.14.5) of Vespasian (69–79 ad). The latter may have been a vectigal that fullers and/or tanners had to pay when they used urine for their work, not a universal tax.

The tax measures of Caligula have gained more attention in academic research. They are mentioned in Suet. Calig. 40 sq., and can be dated, according to D.C. 59.28.8, to the year 40 ad. In detail, these were (Suet. Calig. 40): 1. tax on edibles; 2. tax of 2.5 percent on litigation and trials; 3. tax of 12.5 percent on the daily income of load carriers; and 4. prostitution tax on active and retired prostitutes, panderers, and even married persons in the amount of the price for one cohabitation. Cassius Dio (see above) adds taxes for taverns, craftsmen, and wage-labor slaves. Nearly all details of these taxes are discussed in academic research, but these are mostly hypotheses without evidence in the sources (cf. Günther 2008: 155–160). The tax on edibles was certainly a portorium, a custom duty for the toll district Rome (cf. Günther 2008: 143–146; not in Wojciech 2015). For the prostitution tax, a long existence has been proposed by some researchers (e.g., McGinn 1989), combining evidence for local prostitution taxes and rather dubious references in late antiquity. It has even been described as a tributum because of the mixture of the terms vectigal and tributum of Suetonius here (cf. above). But Suetonius structures his whole chapter to undermine the authority of the “bad” emperor Caligula. The burden of Roman citizens with “tributa” (which were, in fact, all vectigalia due to the lack of a census list), the reference to socially disdained groups liable to the new taxes, and, last but not least, the grouping of the prostitution business together with the “sacred” and eminent matrimonium (Roman legal matrimony) as the core of the Roman family and society as a whole are more revealing of the rhetorical strategy of Suetonius than of historical facts. So these taxes existed—shortly after the murder of Caligula, they were abolished by Claudius (D.C. 60.4.1; Suet. Claud. 11.3), who even propagated the abolition of the tax on edibles by issuing quadrantes (RIC I²  Claudius 126 [Nr. 85, 87, 89, 91]; cf. Wolters 2005: 513–516)—but details cannot be deduced from the biased evidence.

Customs were omnipresent in the Roman Empire. Under the designation of portorium, later often vectigal in its narrow sense (cf. Kritzinger 2015: 12), a lot of inhabitants of the Roman Empire and Roman citizens were involved in paying customs duties or in administration—either as taxpayers (mostly tradesmen) or within the administration process as tax collectors or state authorities. But the source material for this important factor in the Roman Empire is scattered; only a few texts concern portoria, while the main evidence comes from inscriptions and papyri, and a small amount from numismatics. What is needed, therefore, is a combination of different source methods as well as intense knowledge of the often difficult questions in these so-called auxiliary fields (this is also true for vectigalia in general), and it is understandable that there is no current monograph to replace the monumental study of De Laet 1949. His three-step development of the administration process of portoria—from private custom collection consortia (societates publicanorum) up to Trajanic times to single private custom collectors up to Septimius Severus to public collection afterwards—as well as his strict differentiation between border customs, municipal taxes, and road charges are now challenged by new findings (especially the lex portorii Asiae) and recent, deeper research for some regions of the Empire, e.g. the quadragesima Galliarum (2.5 percent custom duty for the Gaulish provinces) or the portorium Illyricum (Illyrian custom duty) (cf. Ørsted P. 1985; France 2001a; Froehlich 2014; general new model by Kritzinger 2015). Many new questions have also been raised, for example concerning the concrete custom collection process or the epigraphic habits of the collectors of customs; here the article collection Das Zollwesen im Imperium Romanum (2015) gives a good overview of current research.

In principle, customs were an easy matter. At the customs stations in certain districts within the Imperium Romanum or at the outer borders, goods had to be declared, and the tax collectors fixed the customs to be paid in cash at once. But the details were tricky. There was no unified tariff in the Roman Empire. The tariff depended on the customs district or on the goods to be declared: at the outer borders (in the East), the tariff was high, at 12.5 percent or even 25 percent, while internal tariffs fluctuated from 1 to 5 percent, often 2.5 percent. Some goods were measured on their value, while for others, such as slaves, there was a fixed payment tariff due to the difficulties of measurement in a short time (cf. Günther 2015c: 229–233). Basic consumer durables were not liable to customs (cf., e.g., Monum. Ephes. ll. 81–83 = §35; ll. 84–87 = § 37; Ps.-Quint. Decl. Min. 359; further sources cf. Kritzinger 2015: 19 no. 61). From the custom inscriptions discovered, for example, in Ephesos, Kaunos, Andriake, Zarai, Myra, and Palmyra we can derive many other details concerning the collection process (cf. in detail Kritizinger 2015: 19–26, with the different editions), from the declaration to the payment at the toll stations (stationes) (cf. now France and Nelis-Clément 2014; also Matz 2015). Here we see an effective as well as efficient administration in action. So for example the issuing of receipts (for a fee?) had not only the purpose of keeping the taxpayer from having to pay double for goods he had not sold at the local market (Monum. Ephes. ll. 16–20 = §6; cf. also Kritzinger 2015: 20sq.) but also of accelerating the customs measuring procedure, of supporting controls by circitores (circulators) (cf. Günther 2015c: 234–236), and, last but not least, of having a legal document for both parties in case of a legal action. These litigations were often a matter of dispute between collectors and payers of taxes. Up to the reform of Nero in 58 ad, there was only the possibility of laying a claim against the tax collectors directly in Rome before the praetor peregrinus (praetor administering justice among foreigners and between citizens and noncitizens); then a cognitio extra ordinem (extraordinary law suit by official investigation process) in the provinces was allowed. Even the tariff regulations had to be published at every tax station (Tac. Ann. 13,50 sq.; cf. Kritzinger 2015: 45 with further evidence). As for the other vectigalia, special agreements between frequent merchants and the tax collectors seem likely, so there was perhaps no permanent conflict between them.

The staff for the collection process, such as actores (administrator), arcarii (cash caretakers), circitores, contrascriptores (countersigners), scrutatores (scrutinizers), vilici (estate manager), etc., mostly freedmen and slaves, was hierarchically organized, differentiated, and specialized according to their duties and responsibilities. The epigraphical evidence reveals a great number of job titles, careers, “religious” activities, and networks within these familiae publicanorum ([slave] families of the publicans), but no systematic study has been done so far except for certain local districts or regions, or posts (cf. e.g. Aubert 1994; Van Nijf 2008; Froehlich 2014; Günther 2015c: 233–238, all with further literature).

But before customs duties could be levied, there was the leasing procedure. Whereas in the Roman Republic (cf. Badian 1972) the censors leased these (and other public contracts) for a five-year period (lustrum), in the Principate this was undertaken by the praetores aerarii Saturni (praetorians of the Treasury of Saturn) in the end (cf. Corbier 1974). The lease took place after a public auction of the license for certain districts, and was laid down in a contract (pactio) between the state and the leaseholder. Furthermore, the main tariff regulations were published in Rome in a lex portoria (custom duty law), and ideally in the tax districts as well, although Nero had to mandate it with his reform edict in 58 ad. This lex portoria as well as the pactiones (contracts) were not written new in and for every new lease period but were updated, as is clearly seen, for example, in the tax law of Asia. The same is true for the staff at the stations; when there was a change in the tax leaseholder, most of the personnel was not replaced but transferred.

An unsolved problem is the question of how the custom concessions were structured regionally and systematically. The “old” model of De Laet (1949; cf. also Vittinghoff 1953), with a strict differentiation between border customs, municipal taxes, and road charges and between publicans as collectors for border customs and road charges and cities (civitates) responsible for the municipal taxes, has now been challenged (cf. Kritzinger 2015: esp. 30–44; for the publicum portorium Illyirici cf. also Ørsted 1985; Froehlich 2014: 77–83). It is now proposed that the civitates were, in fact, part of the publicum portorium system. Ever since Republican times, Rome had granted the right and privilege of raising taxes to certain civitates. These cities could exact it for themselves but usually did it via publicans. The “new” model thus integrates the civitates (and certain confederacies of cities in the Greek East; cf. Kritzinger 2015: 37 sq.; also Edelmann-Singer 2012) into the system, which was not characterized by borders between publicans and cities with different areas of responsibility (customs vs. municipal taxes) but by districts between two entities (e.g., a civitas or a koinon).

The balance of the lease amount was cleared between bureaus of the tax collectors and the administration in Rome every year, first with the aerarium Saturni, then, after an uncertain date in the second half of the first century ad, with the fiscus Caesaris with the a rationibus (secretary of finance) and his familia Caesaris ([slave] family of the emperor) (cf. Kritzinger 2015: 27sq.). Also with the institution of special procuratores, as for the other vectigalia (see above), probably with the reform of Nero, the control of the tax collection process and the collectors shifted to an even more specialized administration. This was the precondition for a step-by-step change concerning the tax collection in the second and third centuries ad. Although there was certainly no reform edict by which private tax collectors were replaced by imperial procuratores and their staff, one finds imperial officials responsible, among other things, for the collection of the publicum portorium Illyrici, perhaps as a preparation for or result of the Marcomannic Wars of Marcus Aurelius (cf. Kritzinger 2015: 46–48; esp. Ørsted 1985: 349 ss.). As for the other vectigalia, these changes were dependent on certain contexts and situations.

Although much has been achieved in revealing Roman taxation policy and organization, there are some fields which can be developed deeper and further. Up to now, researchers have often treated the different taxes and customs individually rather than together. With the new findings, especially the customs laws in the Greek East, questions can be addressed about the collection process for portoria but also—assuming there are analogies and parallel structures in other vectigalia, e.g. efficient structures around the stationes—about the hierarchical structure of the staff, the context-specific but not general replacement of private tax collectors by imperial officials, and even the cooperation between them.

It should, for instance, be possible to solve the interesting question of why the Roman state gave up its basic principle (not only concerning taxes) never to change running systems and shifted the risk of tax collection to private companies by integrating modern theoretical approaches into the study of the Roman tax system. Even though the use of the New Institutional Economics is now being broadly discussed in the Ancient Economy Studies (see Droß-Krüpe et al. 2015), there has been no current application of the basic principles of institutions forming (economic) decisions of people, transactions costs, and principal-agent theory. The establishment of procuratores for the various vectigalia and their step-by-step involvement in the tax collecting process, as well as the replacement of private tax collectors for the tributa, could be explained by the reduction of transaction costs, mainly imbalances in information between the state and private companies, high costs for a new administrative apparatus, etc. The organization of the staff at toll stations and the exchange between them (and with other stations) could be investigated using the principal-agent theory. Last but not least, the “new” model of the organization of portoria in districts, based on the region around a civitas (see above), should be seen as an institutional framework, affecting, channeling, and perhaps controlling the flow of commodity and trade routes.

This framing and forming of trade circles connects portoria directly with the Roman economy. Bearing in mind the tax-and-trade model of K. Hopkins (e.g. 1980; 1995/1996; 2000), questions can be asked about the economic development of certain regions and, with an economic-geographical approach, the development of economic areas (cf. Ruffing 2009), as well as the establishment of so-called Special Economic Zones (cf. Günther forthcoming 2015b) with special rules for economic stimulation, not only concerning taxes and charges.

Furthermore, the effects of taxes on other structural parts of the Roman Empire should be questioned again, and more deeply. If you understand taxes as an open “system” in N. Luhmann’s sense, it could influence the environmental surroundings as well as other “systems” like society and law, and vice versa. So the influence of the inheritance tax on the Roman family (cf. esp. Gardner 2001) could be investigated again by taking into account the effects on the Augustan family laws, or the interdependence between the inheritance tax and legacies as alimenta for life (Dig. 35.2.68) could be investigated with the focus on private donators of alimenta. Finally, the presentation of tax measurements in various media (cf. for the coins Wolters 2005), especially in literary texts, should be analyzed systematically with a keen eye for the “construction” of “good” and “bad” emperors. Because it was they who were, in fact, the beginning and the end of taxes in the Roman Principate.