Socii

200px|thumb|Roman Italy around 100 BC. Roman Cives in green, Latini in red, Socii in orange. The socii ( ) or foederati ( ) were confederates of Rome and formed one of the three legal denominations in Roman Italy (Italia) along with the core Roman citizens (Cives Romani) and the extended Latini. The Latini, who were simultaneously special confederates (Socii Latini) and semi-citizens (Cives Latini), derived their name from the Italic people of which Rome was part (the Latins) but did not coincide with the region of Latium in central Italy as they were located in colonies throughout the peninsula. This tripartite organisation lasted from the Roman expansion in Italy (509-264 BC) to the Social War (91–87 BC), when all peninsular inhabitants south of the Po river were awarded Roman citizenship.

Treaties known as foedus served as the basic template for Rome's settlement with the large array of tribes and city-states of the whole Italian peninsula. The confederacy had its origin in the foedus Cassianum ("Treaty of Cassius", 493 BC) signed by the fledgling Roman Republic with its neighbouring Latin city-states shortly after the overthrow of the Roman monarchy in 510 BC. This provided for mutual defence by the two parties on the basis of an equal contribution to the annual military levy, which was probably under Roman overall command. The terms of the treaty were probably more acceptable to the Latins than the previous type of Roman hegemony, that of the Tarquin kings, as the latter had probably required the payment of tribute and not a simple military obligation.