The origins of the Cathedral of Santhià are very ancient: it was born in the Romanesque period, but it rises on the vestiges of pagan times; according to the pagan tradition, it was in this place that we met for the cult of the God Aesculapius, god of medicine. The crypt of Santo Stefano is the oldest point of the Cathedral, as evidenced by the capitals belonging, according to scholars, to the original pagan temple. The current Collegiate Church of Sant'Agata was built between 1836 and 1839, based on a project by the architect Giuseppe Talucchi. The façade is in neoclassical style and is characterized by a large pronaos supported by six columns, with vaults frescoed by the painter Luigi Hartmann. The interior is divided into three naves, separated by two colonnades, while the frescoes on the vaults and on the walls, depicting episodes from the life of Sant'Agata, were made by Paolo Emilio Morgari, Luigi Hartman and Carlo Costa at the end of the 19th century. . The bell tower, in Romanesque style (dating back to the 12th century), is about 35 meters high. However, what we can see today are only the remains of a taller bell tower, the end of which was knocked down in 1555 by some cannon shots.