Knights of Calatrava (käläträˈvä) [key], Spain's oldest military order, whose original seat was the now ruined fortress of Calatrava la Vieja in Ciudad Real prov., central Spain. Founded (1158) by the Cistercians as a defense against the Moors, the order was very powerful, holding large possessions until the 13th cent.; later it declined. In 1499 the title of grand master passed to the Castilian crown and thence to the Spanish crown.
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