The Renaissance structure of the Lower Church, which houses the Diocesan Museum in Turin, is characterized by the perimeter walls, with rectangular windows that illuminate the interior and emerge on the square, and by the large central pillars that hold up the vaults.
In the centre of the vaults is depicted the coat of arms of Cardinal Domenico Della Rovere of Vinovo that built the Renaissance cathedral in 1491.
In the middle you can see an oak, symbol of the family name, next to which appear the letters "S" and "D", the initials of the cardinal motto "Soli Deo" (to God alone).
The shield is surmounted by a cardinal's hat with cord and side tassels. The plan of the Lower Church faithfully reproduces the Upper Church one: a Latin cross with three naves, with the arms of transept and choir of the same size and shape.
From the sixteenth century until the early nineteenth century, before the construction of the sepulchers of Superga and the chapel of the Holy Shroud, this place was used to house the Archbishops, the Turin's great characters and the Savoys remains, as evidenced by the large crosses recently found on the walls.
After several structural changes, occurred in five hundred years, the spaces of the Cathedral have been restored to their former beauty; thanks to this careful restoration it was possible to recover some fragments of the original floor of the church damaged by some interventions designed to obtain space for a theater and a gym during the twentieth century.
Archaeological excavations have also brought to light the remains of the primitive episcopal complex in Turin, consisting of the three churches of the Savior, St. John the Baptist and St. Mary de dompno (IV-VII century ), as well as some ancient tombs.