A complex of churches
The most notable thing about this church is the fact that it is not really one church, but rather a complex of several: Church of the Cross, Cloister of St. Stephen, Martyrdom of St. Stephen, Saints Vitale and Agricola, and Holy Sepulchre. It is believed that it was originally built to copy the Holy Sepulchre of Jerusalem. From the square you have a great view, so you can see the variety of styles on display. In the area outside are two medieval sarcophagi where the remains of the first two bishops of the Church of Bologna lie. The Basilica of St. Sepulchre is the oldest, I've uploaded a photo of the interior which is very dark, but truly remarkable, the materials used include a column of black African marble, probably reused from an earlier building.