Crusader castle system

Timeline

1. c. 1099–1102Frontier of the Kingdom of Jerusalem · Kingdom of JerusalemAfter the Crusaders captured Jerusalem, they converted old Byzantine and Islamic forts in the Jordan Valley and at inland trade-route nodes into early frontier warning and supply points, laying the groundwork for later takeover by the military orders.
2. c. 1101–1110Karak and the Antioch-Tripoli corridor · Kingdom of JerusalemAfter the failure of the 1101 Crusade, Latin rulers accelerated the construction of stone castles along the frontiers of Antioch, Tripoli, and the Kingdom of Jerusalem; the military orders began taking over key nodes, forming a chain of mutually supporting fortresses.
3. c. 1140–1271Krak des Chevaliers · Homs GovernorateMilitary orders such as the Hospitallers developed some castles into permanent garrison, storage, and tax-collection centers, employing concentric defense and control of water sources, becoming the most representative military-administrative complexes of the Latin East.