The Crusader states, also known as Outremer, were a number of mostly 12th- and 13th-century feudal states created by Western European crusaders in Asia Minor, Greece and the Holy Land, and during the Northern Crusades in the eastern Baltic area. The name also refers to other territorial gains (often small and short-lived) made by medieval Christendom against Muslim and pagan adversaries. The Crusader States in the Levant were the Kingdom of Jerusalem, the Principality of Antioch, the County of Tripoli and the County of Edessa.
Beginning in the 7th century, Muslim rulers began expanding their territories into Christian Roman/Byzantine lands, conquering Egypt and the Levant, and gradually taking over all of North Africa, much of Southwest Asia, and most of the Iberian Peninsula. The Eastern Romans, or Byzantines, partially recovered lost territory on numerous occasions but over time gradually lost all but Anatolia and parts of Thrace and the Balkans. In the West, the Roman Catholic kingdoms of northern Iberia launched a series of campaigns known as the Reconquista to reconquer the peninsula from the Arabized Berbers known as Moors (who called it al-Andalus). The conquered Iberian principalities are not customarily called Crusader states, except for the Kingdom of Valencia, despite fitting the general criteria.
Professor Barber indicates that, in the Crusader State of the Kingdom of Jerusalem the Holy Sepulchre was added to in the 7th century and rebuilt in 1022, "after a previous collapse". “In 691-2 Caliph Abd al Malik had built a great dome over the rock here, a place sacred to all three great religions”