Eridu is considered one of the oldest and southernmost of the Sumerian towns. Built on the shoreline of an ancient north Arabian lake, the city acted as a prime entrepot in the prehistoric Ubaid and Protoliterate periods (5500-2900 B.C.). By the Early Dynastic period (2900-2500 B.C.), the city had become largely a cultic shrine. During its heyday, Eridu had access to both Gulf and interior Arabian markets.