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It was a legend. No trace of the city had ever been found, and it appeared only in a few rare inscriptions and ancient texts. The city of Thonis-Heracleion (known by both its Egyptian and Greek names) was not something anyone was expecting to find, because no one was looking for it. So it was something of a shock when in 2000 French archaeologist Franck Goddio, looking for 18^th-century French warships, saw a colossal face emerge from the watery shadows of the Alexandria bay.

Goddio had stumbled upon Thonis-Heracleion completely submerged 4 miles off the coast of Egypt. Among the underwater ruins were 64 ships, 700 anchors, a treasure trove of gold coins, 16-foot-tall statues, and, most notably, the remains of a massive temple to Amun-Gereb, supreme god of the ancient Egyptians. 

The granite ruins and artifacts are remarkably well preserved. Built around its grand temple, the city was likely criss-crossed with a network of canals—a kind of ancient Egyptian Venice. Its islands were home to small sanctuaries and homes and the city controlled the trade into Egypt. Over 2,000 years ago, Thonis Heracleion was undoubtedly one of the greatest port cities of the world. The question of how it ended up on the floor of the Mediterranean remains unanswered.

More photos of the Lost City of Heracleion can be seen on Atlas Obscura.

Lost cities: 

• Atlit Yam contains the submerged ruins of a neolithic coastal settlement near Atlit, Israel
• Palmyra is a mysterious ruined empire on the Silk Road
• Coronado Heights Castle marks the spot where a conquistador gave up his search for the fabled Seven Cities of Gold

More photos of the Lost City of Heracleion can be seen on Atlas Obscura.