The archpriestal church dominates the centre of Sant Mateu — a great single-nave Gothic building of the 13th and 14th centuries, built on the site of an earlier Romanesque church whose carved portal is still embedded in the south wall. The interior is austere and tall, with simple ribbed vaulting and lateral chapels added during the Baroque era.
The treasury houses some genuinely important medieval silverwork — chalices, processional crosses, and a Gothic monstrance — that survived the wars and church burnings of the 1830s and 1930s thanks to having been hidden. Hours can be erratic; ask at the town's tourist office on the Plaça Major for current access.