It lies on the ancient soil of the city, roughly 5 foot below today's Piazza delle Erbe round level. It is the most ancient church in Mantova. Built by will of Matilde di Canossa it reveals -in its round shape an ideal resemblance with Emperor Costantino's Holy Sepulcher in Jerusalem, a Middle Age world famous masterpiece. The church was deserted in 1579 by order of Duke Guglielmo Gonzaga and shortly thereafter was engulfed by surrounding buildings.
Restoration works began in 1908 and lasted until 1926. Let's step inside in a ring shaped aisle, with narrow stairways hidden within the thick walls, leading in a single flight to the women's gallery above Some Byzantine styled frescoes from the 11th and 12th centuries are still visible, namely a Jesus Christ as the Judge of Life up in the vailt and some rich vested angels on the left side of the main altar.