Foederati (/ˌfɛdəˈrt/, singular: foederatus /ˌfɛdəˈrtəs/) were peoples and cities bound by a treaty, known as foedus, with Rome. During the Roman Republic, the term identified the socii, but during the Roman Empire, it was used to describe foreign states, client kingdoms or barbarian tribes to which the empire provided benefits in exchange for military assistance. The term was also used, especially under the empire, for groups of "barbarian" mercenaries of various sizes who were typically allowed to settle within the empire.