(allies of Rome), after 338 B.C., communities in Italy subject to Rome.

Socii could not conduct an independent foreign policy, had to provide Rome with troops and materiel in wartime, and were obligated to cede part of their lands to Roman colonists. Apart from these obligations in common, socii differed in terms of self-government and rights enjoyed in Rome. Socii Latini nominis (Latin allies) were the most privileged. They enjoyed complete self-government and, at the same time, certain civil rights in Rome. Socii Latini nominis included the cities of Tibur and Praeneste and the Sabine and Volscian cities. Most of the Greek poleis in Italy were socii proper. Their residents had self-government but no rights in Rome. The dediticii were the lowest category of socii, having limited self-government and none of the rights of Roman citizenship. The dediticii included the former members of the Samnite Federation (seeSAMNITES) and, subsequently, Gauls.

The question of granting socii the rights of Roman citizenship was debated in Rome from the time of the Gracchi in the second half of the second century B.C.; however, the question was settled only by the Social War (War of the Allies). As Rome emerged as a Mediterranean power, the Romans came to grant, as a kind of privilege, the rights of socii to individual provincial subjects and entire communities. From the end of the second century A.D., the Roman emperors recruited barbarian tribes for military service and settled them in frontier regions with the status of foederati (federates).

Rome conferred the title socius et amicus populi Romani (ally and friend of the Roman people) on rulers of friendly vassal kingdoms, for example, King Masinissa of Numidia.