St. Zeno died in 380. According to legend, over his tomb, along the Via Gallica, the first small church was erected by Theodoric the Great, king of the Ostrogoths. The history of the present basilican and the associated Benedictine monastery begins in the 9th century,when Bishop Ratoldus and King Pepin of Italy attended the translation of the saint's relics into the new church. This edifice was damaged or destroyed by a Magyar invasion in the early 10th century, at which time Zeno's body was moved to the Cathedral of Santa Maria Matricolare: it was soon moved back to its original site in what is now the crypt of the present church (May 21, 921).
In 967, a new Romanesque edifice was built by Bishop Raterius, with the financial assistance of the Holy Roman Emperor, Otto I. On January 3, 1117 the church was damaged by an earthquake, and as a result was restored and enlarged in 1138. The work was completed in 1398 with the reconstruction of the roof and of the Gothic-style apse. [...]
The interior of the church is on three levels with an extensive crypt on the lower level, the church proper and a raised presbytery. [...] The central church, known as Chiesa plebana, is of the Latin Cross shape with a nave, two aisles and transept. The aisles are divided by cruciform pilasters with alternating capitals with zoomorphic motifs and of Corinthian style. The walls above the colonnade are polychrome. The trefoil-arched wooden ceiling dates from the 14th century.".