Rome dominated its Latin and Italian neighbours by incorporating some into the Roman citizen body and by forming bilateral alliances with most of the Italian city-states.

After the Punic Wars, Rome undertook to rule newly acquired territories directly as subject provinces. In 241 Sicily became Rome's first province, followed by Sardinia-Corsica in 238, and Spain, divided into two provinces, in 197. After a 50-year hiatus, Macedonia and Africa were annexed in 146, and the province of Asia (northwestern Anatolia) in 133.

In principle, each province was to be administered in accordance with its lex provinciae, a set of rules drawn up by the conquering commander and a senatorial embassy. The lex provinciae laid down the organization of taxation, which varied from province to province. The provincial administrative apparatuses were minimal and unprofessional, as the Romans relied heavily on the local elites as mediators. Each year a senatorial magistrate was sent out to govern with nearly unfettered powers. Because initially the governors were usually praetors, the addition of new provinces required the election of more praetors (increased to four in 227 and to six in 197).

The assignments to provinces were done by lot. The governor took with him one of the quaestors to oversee the finances of provincial government and senatorial friends and relatives to serve as deputies and advisors (legati). Among the humbler functionaries assisting the governor were scribes to keep records and lictors with fasces (bundles of rods and axes) to symbolize gubernatorial authority and to execute sentences pronounced by the governor in criminal cases. The governor's main duties were to maintain order and security and to collect revenues. The former often entailed command of an army to ward off external threats and to suppress internal disorders such as banditry. When not commanding his army, the governor spent his time hearing legal cases and arbitrating disputes.

During the republic, revenue collection was left to private companies of publicani, so called because they won by highest bid the contract to collect the revenues. It was the governor's responsibility to keep the publicani within the bounds of the lex provinciae so that they did not exploit the helpless provincials too mercilessly, but this was difficult. Governors expected to make a profit from their term of office, and some collaborated with the publicani to strip the provinces of their wealth.