This book deals with the historical and architectural development of Krak des chevaliers or Hisn al-Fursan in Homs - Syria, the historical and architectural development. There are indications that the beginnings of fortifying the site of this citadel date back to the reign of Thutmose III. Its place was a castle built by Ramesses II, called Shabtun Castle. However, according to historical and archaeological evidence, it was established in the year (1031 AD) and also became known to Arab historians as Fortress of the Kurds. It was occupied by the Crusaders in 1099 AD, and Raymond I, ruler of the Emirate of Tripoli, in 1142 AD, gave it to the Hospitaller military monks. It was called the Castle of the Knights, as was Al-Zahir Baybars (1171 AD) and Sultan Qalawun (1285 AD).The book aims to conduct an analytical study of the architectural elements of Al-Hosn Citadel in Homs to highlight the historical stages that the citadel went through and the Seljuk, Crusader, and Mamluk renovations, following the descriptive and analytical approaches to identify the architectural elements for each of the historical periods that the citadel went through.