The Co-cathedral of Santa María la Mayor was originally built in the 13th century on the site of an earlier mosque, then substantially rebuilt and expanded over the following centuries. It became a co-cathedral in 1959, sharing diocesan responsibility with Sigüenza cathedral. The building is a patchwork of Gothic, Renaissance, and baroque additions that reflects the long, interrupted history of its construction.
The interior is large and somewhat austere. The main chapel contains an important collection of religious art, including works from the 16th and 17th centuries. The exterior west façade, facing the Plaza de la Infanta, is the most coherent architectural statement — a baroque composition added in the 18th century.