The Kasbah of the Udayas is a kasbah in Rabat, Morocco at the mouth of the Bou Regreg river opposite Salé. It was built during the reign of the Almohads (AD 1121-1269). When the Almohads had captured Rabat and destroyed the kasbah of the Almoravids in the town, they began reconstructing it in AH 544 / AD 1150. They added a palace and a mosque and named it al-Mahdiyya, after their ancestor al-Mahdi Ibn Tumart. After the death of Yaqub al-Mansur (AH 595 / AD 1199) the kasbah was deserted.