Hassan Tower or Tour Hassan (Arabic: صومعة حسان‎) is the minaret of an incomplete mosque in Rabat, Morocco. Begun in 1195 AD, the tower was intended to be the largest minaret in the world along with the mosque, also intended to be the world's largest. In 1199, Sultan Yacoub al-Mansour died and construction on the mosque stopped. The tower only reached 44 m (140 ft), about half of its intended 86 m (260 ft) height.

Source: Wikipedia - Hassan Tower