first basilica of St. Peter's in Rome, a five-aisled basilican-plan church with apsed transept at the west end that was begun between 326 and 333 at the order of the Roman emperor Constantine and finished about 30 years later. The church was entered through an atrium called Paradise that enclosed a garden with fountains. From the atrium there were five doors into the body of the church. The nave was terminated by an arch with a mosaic of Constantine, accompanied by St. Peter, presenting a model of his church to Christ. On the clerestory walls, each pierced by 11 windows, were frescoes of the patriarchs, prophets, and Apostles and scenes from the Old and New Testaments. Old St. Peter's was torn down in the early 16th century and replaced by New St. Peter's (see Saint Peter's Basilica).