Aguilar Castle stands on a rocky hillock at the foot of the prestigious Haut Fitou vineyard. It is one of the "five sons of Carcassonne" which, in the 12th century, watched over the frontier with what was then Spain. It was owned successively by Catalan counts, by Viscounts of Carcassonne and, at the time of the Crusade, by Olivier, Lord of Termes. In 1210 it was captured by Simon de Montfort and then fell into the hands of the King of France, Louis IX. It was consolidated and modified by royal engineers at the end of the 13th century. Its upper bailey has some architectural features that are quite unique in this region.