The Romanesque belfry, standing at some 67 m, was erected over an ancient Lombard tower.

It is the seat of the Bishop of Pistoia and is dedicated to Saint Zeno of Verona. Most probably built in the 10th century, it has a façade in Romanesque style, inspired by other churches in Pistoia (San Bartolomeo and San Jacopo). The interior has a nave and two side-aisles, with a presbytery and crypt. A restoration in 1952-1999 returned the church to its original lines (Baroque additions removed). Between 1379 and 1440 the façade was reconstructed with the addition of three tiers of loggias and a portico. In 1504 Andrea della Robbia was commissioned to undertake the decoration of the archivolt and portal.