Next to the Victor Emmanuel Monument, on Via Del Teatro di Marcello, you will find these ruined apartment blocks, dating back to Imperial Rome. Looking rather like a comb of condos, it's amazing to see these ancient warrens.
This ancient Roman is the only survivor in Rome, and dates from the 2nd century A.D. It had at least 6 floors. In the Middle Ages, a section of the upper storeys was converted into a church.