What is Ambitus?

Legal Definition
In ancient Roman law, ambitus was a crime of political corruption, mainly a candidate's attempt to influence the outcome of an election through bribery or other forms of soft power. The Latin word ambitus is the origin of the English word "ambition," which is another of its original meanings; ambitus was the process of "going around and commending oneself or one's protégés to the people," an activity liable to unethical excesses. In practice, bringing a charge of ambitus against a public figure became a favored tactic for undermining a political opponent.

The Lex Baebia was the first law criminalizing electoral bribery, instituted by M. Baebius Tamphilus during his consulship in 181 BC. The passage of Rome's first sumptuary law the previous year suggests that the two forms of legislation are related; both were aimed at curbing wealth-based inequities of power and status within the governing classes. The temptation to indulge in bribery indicates that the traditional patron-client relationship was insufficient to gather enough votes to win election.

The word ambitus for electoral corruption is a general term for the crime; defendants would have been charged under a specific statute (lex). The 2nd-century BC Greek historian Polybius, a major source on the workings of the Roman constitution, makes the extravagant assertion that while Carthaginians acquire public office by openly offering gifts, the penalty at Rome for doing so is death. The point is perhaps that ambitus could be construed as treason under some circumstances.

The rhetorical tactics of Cicero's speeches demonstrate how an initial charge of ambitus, under whatever statute, might devolve into an occasion for impugning or humiliating a public figure. Popularist politicians were particularly vulnerable to charges of currying favor with the masses, and ambitus might be alleged when a man of lower social rank defeated his superior in an election: "The defeat of a candidate boasting nobilitas by another not in possession of such standing appears to have been sufficient grounds for initiating a charge of ambitus."

During the Imperial era, the ambitious politician yielded of necessity to the bureaucrat in the holding of Roman magistracies. The Stoic philosopher Epictetus (1st–2nd centuries AD) recoiled from the rough-and-tumble of electoral politics and ambitus:

For the sake of these mighty and dignified offices and honours you kiss the hands of another man's slaves — and are thus the slaves of men who are not free themselves. … If you wish to be consul you must give up your sleep, run around, kiss men's hands, rot away at other men's doors … send presents to many and daily xenia [guest-gifts] to some. And what is the result? Twelve bundles of rods, sitting three or four times on the tribunal, giving games in the Circus, and distributing meals in little baskets.

Bribery of a person already holding office was covered by laws de repetundae; provincial governors were particularly susceptible to such charges.
-- Wikipedia
Legal Definition
In the Roman law. A going around; a path worn by going around. A space of at least two and a half feet in width, between neighboring houses, left for the convenience of going around them. Calvin. The procuring of a public office by money or gifts; the unlawful buying and selling of a public office, Inst. 4, 18, 11; Dig. 48, 14.
-- Black's Law Dictionary