The Basilica of Maxentius (also known as the Basilica Nova), which stands in the Forum Romanum, was begun in 308 by the emperor Maxentius (r. 306-12) and completed (with major modifications) by his co-emperor Constantine I (r. 306-37).
The enormous building, the largest ever erected in the Forum, was 100 metres long and 65 metres wide. However, all that survives of it are three vast barrel-vaulted spaces, each 20.5 metres wide, 17.5 metres deep and 24.5 metres high, which formed the north side of the basilica. The vaults are decorated with weight-saving octagonal coffers.
The main body of the basilica rose to a height of 35 metres and its three groin-vaults had a span of almost 20 metres!
The interior walls of the basilica were faced with marble and stucco. The eight Corinthian columns, each 14.5 metres high, which stood in the central section, have disappeared, apart from one, which was moved by Pope Paul V (r. 1605-21) to Piazza Santa Maria Maggiore, where it still stands.
A colossal acrolithic statue of Emperor Constantine I graced the west apse. Remains of the statue were unearthed at the end of the 15th century and are on display in the courtyard of Palazzo dei Conservatori.