Calatayud (; 2014 pop. 20,658, declining along the last decade due to migration) is a
municipality in the
Province of Zaragoza, within
Aragón, Spain, lying on the river
Jalón, in the midst of the
Sistema Ibérico mountain range. It is the second-largest town in the province after the capital,
Zaragoza, and the largest town in Aragón other than the three provincial capitals. It is the seat of the
comarca of
Calatayud.