The Church of San Pietro is the most ancient Church in Gallarate.

It was built between the 11th and the 13th century by the Comacini masters,  its architectural style is Romanesque with Gothic elements, its interior has a single nave.

Over the centuries, it has undergone several modifications such as the building of a bell tower, the building of side apses, the enlargement of the central one, the opening of Baroque windows, the relocation of the entrance door and other changes that have ruined its primitive beauty. In the 15th century it was turned into a fortress and was later used for other purposes, such as meeting place, carpenter's shop and butcher's shop. 

In 1844 it was declared a national monument; from 1897 to 1911 restoration work was carried out, which consisted of the demolition of the bell tower and the houses leaning against the church, the reconstruction of the old wooden roof and the original apse, and the decoration of the interior walls. On 28 October 1911, the church was re-consecrated.