Ajloun Castle is a 12th-century Muslim castle situated in northwestern Jordan. It is placed on a hilltop belonging to the Jabal Ajloun "Mount Ajloun" district, The name 'Ajloun goes back to a Christian monk who lived on this mountain in the Byzantine Period The castle stands on the ruins of a monastery, traces of which were discovered during archaeological excavations.
The castle has been the nucleus of a settlement which has grown to become the present town of Ajloun. The castle's developing faubourg led to its second name, Qal'at ar-Rabad, "the castle of the faubourg" or "the castle with the suburbs". This name still resonates in the surname of a large and reputable Christian family owning most of the agricultural lands in the direct vicinity of the castle until this day, the Al-Rabadis.
The original castle had four corner towers connected by curtain walls and a double gate. Arrow slits were incorporated in the thick walls and it was surrounded by a moat averaging 16 meters (about 52 feet) in width and 12–15 meters (about 40–50 feet) in depth.