Arsuf, also known as Arsur or Apollonia, is an ancient city and fortress in Outremer, on a cliff above the Mediterranean Sea. In 640, the town was captured by Muslims. The town's area decreased, and for the first time it was surrounded by a fortified wall with buttresses, to resist the constant attacks of Byzantine fleets from the sea. Large marketplaces appeared, and a large scale pottery production center was established. In 809, following the death of Harun al-Rashid, the city fell to the Emirate of Damascus.