Side was a city of Pamphylia and a metropolis from the 5th century. Excavation has revealed a detailed picture of urban development. Side occupied a peninsula defended by walls restored in late antiquity. Colonnaded streets led from the main gate to the agora and theater, thence past churches and gymnasia to a large basilica on the harbor; the civic buildings were extensively restored by comites and various municipal officials called pater poleos in the 4th-6th century. This period saw the construction of a new bath and of a large complex of cathedral, bishop's palace, and associated buildings. Unfortunately, the chronology of most buildings has not been determined. Side also had a synagogue that served its Jewish community. Around 390 Amphilochius of Iconium convoked a large council in Side to condemn Messalianism. Photios read its minutes, which are now lost. It has been suggested that the council had convened in the 5th century and was presided over by Amphilochios of Side, a correspondent of Cyril of Alexandria, but his conjecture was rejected.

Side flourished through the 6th century but contracted thereafter, when a new fortification wall included only half the urban area. The Byzantine churches of Side, which include some of the first examples of the inscribed-cross plan, are tiny compared with earlier churches: one of them was built within the nave of the ruined harbor basilica. Sources of the 11th century describe Side as abandoned.