Started in 1231 by Blanche de Castille, regent and mother of St Louis, the fortress is a splendid example of medieval architecture, covering 25,000m/82,000ft2 within its ramparts, bordered by a dry moat or the cliff edge and linking 17 towers. In a purpose-built gallery, the world-famous Apocalypse Tapestry is the oldest example of a work on this scale to have survived.