What were the Pillars of Hercules?

This is the name by which ancient people knew the Strait of Gibraltar, the narrow body of water which connects the Mediterranean Sea and the Atlantic Ocean. One of the pillars is Gibraltar. The other massive promontory lies across the Strait on the African coast (probably Mount Acho, just east of Ceuta). The Strait is about 58 km long, and at its narrowest point only 14 km wide. The width between the ancient Pillars of Hercules is 22 km. Legend claimed that the pillars were rocks torn asunder by the Greek hero Hercules, in order to open the Atlantic Ocean into the Mediterranean. Other myths related how Hercules once joined them to make a bridge, or fixed them to narrow the Strait, so as to keep out the monsters of the deep.