Ajlun Castle is located on the site of an old monastery. It was built in 1184 by Izz al-Din Usama, a general in the army of Saladin. The castle controlled traffic along the road connecting Damascus and Egypt.
The fortress marks the furthest limit of Frankish incursions during the Crusades. The Mamluks added a prominent tower to the castle. It was captured by the Mongols in 1260 and was partially destroyed in the process.