Montreal was a Crusader castle located in "Idumaea" (Edom) on the eastern side of the Jordan river. The ruins, called Shaubaq in Arabic, are located in modern Jordan.

The castle was built in 1115 by Baldwin I of Jerusalem during his expedition to the area (during which he captured Aqaba on the Red Sea in 1116). It was strategically located on a hill on the plain of Edom, along the pilgrimage and caravan routes from Syria to Arabia. This allowed Baldwin to control the commerce of the area, as pilgrims and merchants needed permission to travel past it. It was surrounded by relatively fertile land, and two cisterns were carved into the hill, with a long, steep staircase leading to springs within the hill itself.

It remained property of the royal family of the Kingdom of Jerusalem until 1142, when it became part of the Lordship of Oultrejordain. At the same time the centre of the Lordship was moved to Kerak, a stronger fortress to the north of Montreal. Along with Kerak, the castle owed sixty knights to the kingdom. It was held by Philip de Milly, and then passed to Raynald of Chatillon when he married Stephanie de Milly. Raynald used the castle to attack the rich caravans that had previously been allowed to pass unharmed; he also built ships there, then transported them overland to the Red Sea, planning to attack Mecca itself. This was intolerable to the Ayyubid sultan Saladin, who invaded the kingdom in 1187. After capturing Jerusalem, later in the year he besieged Montreal; during the siege the defenders are said to have sold their wives and children for food, and to have gone blind from "lack of salt." Because of the hill Saladin was unable to use siege engines, but after almost two years the castle finally fell in May of 1189. (The defenders' families were returned to them.)

The Mameluks later captured and rebuilt it; little remains of the original Crusader fortifications. Although it has never been fully excavated, it is known that there was a set of three walls, which partially remain.