The Ben Youssef Mosque (also known by its English spelling as the "Ibn Yusuf Mosque"), is a mosque in the medina quarter of Marrakesh, Morocco, named after the Almoravid emir Ali ibn Yusuf. It is arguably the oldest and most important mosque in Marrakesh. Having fall into ruin in the course of the 17th and 18th Centuries, it was almost completely rebuilt in early 19th Century by the Alaouite sultan Suleiman, with hardly any trace left of its original Amoravid or Almohad design.