Impossible to miss, this is the massive brick building standing in the Forum Romanum and showing some of its vaults along the Via dei Fori Imperiali. Work began under Maxentius in 305, and was completed by Constantine. This grandiose building housed the huge statue of Constantine (a few fragments of this statue are displayed in the Palazzo dei Conservatori courtyard). The building's gilded bronze tiles were used on the roof of St Peter's Basilica.