Gibraltar is a British Overseas Territory and headland, on Spain's South Coast.  It's dominated by the Rock of Gibraltar, a 426m-high limestone ridge.  First settled by the Moors in the Middle Ages and later ruled by Spain, the outpost was ceded to the British in 1713.  Layers of fortifications include the remains of a 14th-century Moorish Castle and the 18th-century Great Siege Tunnels, which were expanded in WWII.  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.  Since the 18th-century, Gibraltar has been a symbol of British naval strength, and it is commonly known in that context as "The Rock".