Hippo Regius is the ancient city that underlies modern Annaba — a Phoenician foundation that became one of Roman Africa's most important ports and the see of Christianity's most influential theologian. The archaeological site lies about 2 kilometres southwest of the city centre, and the ruins are substantial: a Roman forum, public baths, private villas with mosaic floors, and a Christian basilica foundation thought to be the cathedral where Augustine preached.
An on-site museum houses mosaics recovered from the excavations, portrait busts, and a small collection of inscriptions. Most visitors come for the Augustine connection, but the site is genuinely impressive independent of that — the scale of the forum and the quality of the mosaic work make clear how wealthy and cosmopolitan Hippo Regius was at its peak. The ruins are partially shaded and not heavily visited, which makes for a quiet and unhurried visit.