The first San Fermo Maggiore was built in the eighth century in memory of saints Fermo and Rustico, believed at the time to have been martyred in the arena.

 It was replaced in the 11th century with the present structure, and the crypt is the only surviving part of the original. The current church retains its 11th-century Romanesque lower portion, with a Gothic upper section from the 13th-14th century. 

The facade is beautifully decorated in marble. The church houses a 14th-century wooden crucifix and Alessandro Turchi's Adoration of the Shepherds.