Hassan Tower is the incomplete minaret of what would have been the largest mosque in the western Islamic world — started in 1195 by Almohad sultan Yacoub al-Mansour and abandoned at 44 metres when he died. The mosque itself never rose above its column stumps, which still stand across the plateau in ordered rows. Facing the tower across the esplanade is the Mausoleum of Mohammed V, a 20th-century masterwork of Moroccan craftsmanship with a green-tiled pyramid roof. The whole site is part of the UNESCO-inscribed historic ensemble of Rabat.