On the top of the large rock which dominates the population, sits the majestic ´Colegiata de Santa María la Mayor´. The Collegiate was built in Romanesque style, and was a former Muslim fortress. The population owes its name to the castle or ´Al-Qasr´ built to defend access to Barbastro.
 
In 1099, King Sancho Ramirez gave Alquézar a community of Augustinian canons and for this reason they built a collegiate church on the campus of the old castle of the Muslim era.