The Rock of Gibraltar, at the southwestern tip of Europe, is a mass of limestone which was elevated over millions of years as Africa pushed into Europe. The result of this accident of Nature was the creation of one of the world’s most stunning geological monuments. In classical times it was one of the Pillars of Hercules, marker of the end of the world. In time this geological monument became a natural fortress. With the British capture of Gibraltar in 1704 it became the Fortress of Fortresses.