It encompassed an extensive and partly undefined region to the east of the Jordan River, and was centered on the castles of Montreal and Kerak.

Baldwin also invaded again in 1107 and 1112, and built Montreal in 1115 to control the Muslim caravan routes, which provided enormous revenue to the kingdom.

Many of the Syriac Orthodox Christians who lived there were transplanted to Jerusalem in 1115 to fill up the former Jewish quarter (the Jews had been either killed or expelled).

It was established after the expedition of Baldwin I, but due to the relative size and inaccessibility of the area, the lords of Transjordan tended to claim some independence from the kingdom.

Philip joined the Knights Templar in 1165, leaving the lordship to his daughter Helena and son-in-law Walter III Brisebarre.

In 1229 Jerusalem was briefly recovered by treaty by Emperor Frederick II, but the remnant of the kingdom never again controlled territory to the east of the Jordan.

The principality was of course claimed by crusader nobles for a long time, the title passing to the line of Isabella of Toron, daughter of Stephanie, and for several generations belonged to Montfort family, who were lords of Tyre.

After the 1350s, when the Montfort line became extinct without close heirs, the hereditary rights presumably passed to the kings of Cyprus who also were descendants of lords of Toron and Tyre.