Heracleion is also a spelling of Heraklion, Crete's largest city and capital. Heracleion (Greek: ἡράκλειον), also known as Thonis (θῶνις), was an ancient Egyptian city near Alexandria whose ruins are located in Abu Qir Bay, currently 2.5 km off the coast, under 10 m (30 ft) of water.eracleion was originally built on some adjoining islands in the Nile Delta, and was intersected by canals. It possessed a number of harbours and anchorages, was the sister city of Naucratis, and was superseded by Alexandria.