It appears that the original site of the city was abandoned for centuries after the Umayyad conquest of Tunisia: https://en.wikipedia.org/wiki/Battle_of_Cartha

It appears that the original site of the city was abandoned for centuries after the Umayyad conquest of Tunisia: https://en.wikipedia.org/wiki/Battle_of_Carthage_(698) https://en.wikipedia.org/wiki/Battle_of_Carthage_(698) Tunis was founded across the lake as a replacement shortly thereafter, and development shifted there probably for land availability and protection from naval attacks.