The territory of Vatican City is part of the "Mons Vaticanus" (Vatican Hill), and of the adjacent former Vatican Fields, where St. Peter's Basilica, the Apostolic Palace, the Sistine Chapel, and museums were built, along with various other buildings. The area was part of the Roman rione of Borgo until 1929. Being separated from the city on the west bank of the Tiber, the area was a suburb that was protected by being included within the walls of Leo IV, later expanded by the current fortification walls of Paul III, Pius IV, and Urban VIII.