Duncan's book is...not very good. No, I'll say it. It's bad. I could barely make it through about two pages before I realized that it was basically just Duncan repeating Appian and Plutarch without any critical analysis and with next to no understanding of the scholarly literature. I suppose that at the very least Duncan is pretty up-front about the fact that he's not writing a book about the Romans at all, but about what he thinks the US is like, which is more than could be said about Holland, but that's mostly through interviews, he tries to disguise it as much as possible in the book. Unsurprisingly it doesn't have any reviews from classicists, who typically aren't aware of it (with good reason), but in reference to this sort of thing I quite like the sole reference to Tom Holland's work, which is basically exactly the same thing, in the BMCR, which lists Holland alongside Farrokh for not even being aware of the so-called "Iranological Revolution," a major paradigm shift in the scholarship of ancient Persia. It's a typifying remark.

I had to pull up a Google Books preview to figure out precisely what Duncan is talking about, since "joint-stock companies" is a shorthand that you'll find is used to refer to a number of Roman economic activities. Apparently he's talking about publicans. Duncan describes publican companies as groups of men buying shares in the company and then bidding on the rights to state contracts as a joint-stock company. Tellingly, he then starts referring to the publicans as "corporations," which pretty clearly shows where he's going with this.

Duncan makes a number of errors in this section, along with telling a very straightforward narrative of a problem that is in fact much-debated by scholars of Roman economics and law. First, he incorrectly defines the equestrians, claiming that the Augustan definition of the equites as those individuals who possessed fortunes of at least 400,000 sesterces (the plural of which, for some reason, he thinks is "sesterce") is a definition that was already in place during the time of the Gracchi. We don't know that, and it doesn't actually appear to be the case--equites was a term used quite freely around the time of Cicero, who often seems to use it to mean people who qualify for senatorial magistracy by wealth but who abstain from politics (see also Lucilius' self-definition of himself as an equestrian, though members of his family were senatorial and his brother likely held a spot in the senate). Duncan also mistakenly attributes the existence of publicans to the fact that senators could not do business. While senators were, strictly speaking, barred from business pursuits and had been since the Lex Claudia in 218, they were first of all not barred from making money via business (slaves and freedmen could operate businesses for their senatorial masters in their stead) and the prohibition against senatorial business had nothing to do with the publicans, who procured funds and took care of other logistical matters for the state, not for individual senators. The Roman state saw no problem with the senate or senatorial magistrates dealing with money and logistics. The senate, traditionally, controlled the magistrates of the mint, set in order the income received from foreign sources (which is what, Stockton showed decades ago, got Ti. Gracchus in trouble, when he promulgated a plebiscite to distribute Attalus' fortune instead of letting the senate do it), and so forth. The lowest senatorial magistracy of the classical cursus honorum, the quaestorship, was tasked entirely with the logistical and financial affairs of imperium-wielding magistrates, and the aediles likewise took on many of the same functions within the city itself. Rather, publican contracts existed not because senators could not perform those functions and had to outsource them to equestrians (the BNP entry on publicans, echoing decades of scholarship on the prosopography of publicans, says outright that "The majority of the equites Romani were not publicani, and conversely very few publicani were equites."), but because publicans offered the relatively limited bureaucracy of the Roman state a ready source of manpower to extract state funds. Moreover, it was technically still customary by the first century to assign public funds during censorships, i.e. every five years. This meant that even by the early first century, when the censorship had lost much of its clout and increasingly was not being filled, the tendency was for public funds to be assigned and gathered at intervals, which fit awkwardly into the annual cycle of magistracies. Finally, and perhaps most importantly, the publican contracts were a result of a somewhat archaic habit that the Roman state preserved, namely that public funds were collected by the auction of public property. The extension of the practice to the collection of public funds is pretty natural

The identification of publicans as members of joint stock companies rests on the existence of societates of publicans. The term is not easy to translate, and has a much broader meaning outside of the societates publicorum. According to the Digest, societates publicorum enjoyed particular special rights, along with a handful of other types of associations like the collegia navicularia:

Quibus autem permissum est corpus habere collegii societatis sive cuiusque alterius eorum nomine, proprium est ad exemplum rei publicae habere res communes, arcam communem et actorem sive syndicum, per quem tamquam in re publica, quod communiter agi fierique oporteat, agatur fiat.

To those for whom it is permitted to have a legal body of [such a sort as] a collegium or societas, or of any other sort of those in name, it is lawful that they have common property, on the model of a state ["res publica," in this context a city with set laws, not an entire state like that of the Romans], a common treasury, and an agent of syndicate [the meaning of this phrase is much-debated], through whom, just as in a state, whatever ought to be done or happen communally is done or happens.

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