Castillo de Panillo (also known as Castillo de Pano) is located in the locality of Pano, within the municipality of Graus in the province of Huesca, Aragón, positioned at approximately 1,000 meters altitude in the Sierra de San Martín. Built around 1055–1060, likely by local craftsmen influenced by Lombard architectural traditions, the fortress served as a crucial Christian stronghold in the frontier warfare between Christian and Muslim kingdoms. The complex comprises a fortified enclosure, the castle proper, and a Romanesque church, originally designed to defend key mountain passes. Distinctive military features include narrow gun ports at the base of walls designed to deploy defensive measures against attackers, exemplifying the sophisticated medieval fortress design of Aragón's frontier territories.
