St. Peter's Basilica (Italian: San Pietro in Vaticano) is a major basilica in Vatican City, an enclave of Rome. St. Peter's was until recently the largest church ever built and it remains one of the holiest sites in Christendom. Contrary to what one might reasonably assume, St. Peter's is not a cathedral - that honor in Rome goes to St. John Lateran.
St. Peter's Basilica stands on the traditional site where Peter - the apostle who is considered the first pope - was crucified and buried. St. Peter's tomb is under the main altar and many other popes are buried in the basilica as well. Originally founded by Constantine in 324, St. Peter's Basilica was rebuilt in the 16th century by Renaissance masters including Bramante, Michelangelo and Bernini.