Gibraltar is the key to the Mediterranean Sea. It is 3 miles (5 km) long and 3/4 mile wide and is connected to Spain by a low, sandy isthmus which is 1 mile long.
Gibraltar is a heavily fortified British air and naval base that guards the Strait of Gibraltar, which is the only entrance to the Mediterranean Sea from the Atlantic Ocean (hence called the key).
Gibraltar is considered to have been one of the two Pillars of Hercules, the other being Mount Hacho on the opposite African coast. The Pillars defined the western limits of navigation for the ancient Mediterranean world.