Heracleion, also known as Thonis, was an ancient Egyptian city near Alexandria whose ruins are located in Abu Qir Bay. It was known as early as the 12th century BC but its importance grew during the waning days of the Pharaohs, the late period, when it was Egypt's main port. It was believed that Helen of Troy and Hercules had visited the city, and that the city had even gained its name from Hercules (Herakles in Greek). There was also a large temple dedicated to the Greek hero at the city center. Pharaoh Nectanebo I made many additions to the temple in the 4th century B.C.^[1]

The city sank in the 6th or 7th century A.D., probably due to major earthquakes and floods. The ruins submerged in the sea were finally located and rediscovered by the French underwater archaeologist Franck Goddio in 2000.^[2]