Hmm. On the other hand, the Principate and late Republic had the publicani, which are about as close to corporations as the world was going to get for centuries. "The existence of the societas publicanorum did not - to a large extent - depend on the individuals involved; a representative could act 'for the company;' ownership was fungible, traded in the form of shares and separated from the control of the company."
"We also learn that the shares were traded. In his second speech against Verres (1,55,143), Cicero implies the transferability of shares, when he quotes an exceptional restriction: Qui de L. Marcio M. Perperna censoribus redemerit... socium non admittito neve partem dato neve redimito, i.e. anyone who had been leasing under the censors L. Marcius and M. Perperna was not admitted to the current lease, neither as a partner, nor as a shareholder, nor should he be allowed to buy any shares later. His quote and the context of the case reveal that shares were often traded between participes after the contract had been assigned to a societas publicanorum.
What makes the partes look even more like modern shares - and is additional evidence parties were not just loans with variable interest rate, as proposed by Duff45 - is the mention of variable "stock prices." In P. Vat 12,29 Cicero speaks of partes illo tempore carissimae, of 'shares that had a very high price at that time.' He implies that the value of the shares depends upon the success of the enterprise and was as such subject to fluctuations, just like today's stock market. In fact, the "stock-market jargon" in this and similar quotes have led some scholars to believe that a "stock-market life" existed in Rome.'