The Basilica of San Petronio hosts a sundial in the form of a meridian line inlaid in the paving of the left aisle in 1655. It was calculated and designed by the famous astronomer Giovanni Domenico Cassini, who was teaching astronomy at the University: at 66.8 meters it is the longest sundial in the world, following measurements that were for the time uniquely precise.
The Basilica of San Petronio is the main church of Bologna. It is the fifth largest church in the world, stretching for 132 meters in length and 60 in width, while the vault reaches 45 meters inside and 51 meters in the facade. It can contain about 28,000 persons. The first stone of construction was laid June 7, 1390.