St. Peter's Basilica (Italian San Pietro in Vaticano) is a Catholic major basilica in Vatican City, an enclave of Rome. Within the stronghold of the papacy, the immense building is often described as the largest church ever built and one of the holiest sites in Christendom. Construction on St. Peter's, was begun in 1506 and finished in 1626.
Tradition says it was built at the place where St. Peter, one of the apostles of Jesus Christ and considered the first pope, was crucified or buried. The church, it is said, hosts the tomb of St. Peter under the main altar, which is covered by a baldachin held by four immense pillars, all designed by Bernini. The other popes are also buried in the basilica.
The basilica in itself is an artwork composed of many artistic elements of value, starting with its elements. Construction started under Pope Julius II in 1506 and was completed in 1615 under Pope Paul V. Many famous artists worked on the "Fabrica di San Pietro" (as the complex of building operations were officially called). Michelangelo, who served as main architect for a while, designed the dome.
Few are aware that St. Peter's is not, in fact, a cathedral, i.e. the seat of a bishop. The pope is also the bishop of Rome, but the diocese is traditionally based in the cathedral of St. John Lateran.
Despite a frequent confusion due to the similar names, the church of St. Peter ad Vincula (famous for hosting the precious Michelangelo's "Moses") is a different church, situated on the other side of the Tiber river.