Castell de Sant Joan d'Algars consists of medieval fortress ruins dramatically situated on a hill above the river Algars in Batea, Terra Alta. First documented in 1153 through Count Barcelona's donation charter to the Knights Templar, the visible remains likely date from the thirteenth century, representing the complex's later medieval phases. The Knights Templar controlled the fortress until the order's suppression in the early fourteenth century, after which it passed between feudal lords. Today, the ruins preserve a distinctive pointed Gothic arch, fragments of tower structures, and partial walls scattered across the hillside, with the keep's final corner demolished in 1975. Beside the castle stands the Church of Sant Joan, the original parish church serving the now-abandoned medieval settlement, which has evolved into a modest hermitage. Together, these remnants provide valuable archaeological evidence of Catalan frontier defense architecture and rural medieval settlement patterns in the terra alta region.
