The Papal Basilica of Saint Peter in the Vatican, or simply Saint Peter's Basilica, is a church of the Italian High Renaissance located in Vatican City, an independent microstate enclaved within the city of Rome, Italy. It was initially planned in the 15th century by Pope Nicholas V and then Pope Julius II to replace the ageing Old St. Peter's Basilica, which was built in the fourth century by Roman emperor Constantine the Great. Construction of the present basilica began on 18 April 1506 and was completed on 18 November 1626.

Catholic tradition holds that the basilica is the burial site of Saint Peter, chief among Jesus's apostles and also the first Bishop of Rome (Pope). Saint Peter's tomb is directly below the high altar of the basilica, also known as the Altar of the Confession. For this reason, many popes, cardinals and bishops have been interred at St. Peter's since the Early Christian period.

St. Peter's is famous as a place of pilgrimage and for its liturgical functions. The pope presides at a number of liturgies throughout the year both within the basilica or the adjoining St. Peter's Square; these liturgies draw audiences numbering from 15,000 to over 80,000 people St. Peter's has many historical associations, with the early Christian Church, the Papacy, the Protestant Reformation and Catholic Counter-Reformation and numerous artists, especially Michelangelo. As a work of architecture, it is regarded as the greatest building of its age.

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Saint Peter's Square is a large plaza located directly in front of St. Peter's Basilica in Vatican City, the papal enclave in Rome, directly west of the neighborhood (rione) of Borgo. Both square and basilica are named after Saint Peter, an apostle of Jesus whom Catholics consider the first Pope.

At the centre of the square is the Vatican obelisk, an ancient Egyptian obelisk erected at the current site in 1586. Gian Lorenzo Bernini designed the square almost 100 years later, including the massive Doric colonnades,[1][2] four columns deep, which embrace visitors in "the maternal arms of Mother Church". A granite fountain constructed by Bernini in 1675 matches another fountain designed by Carlo Maderno in 1613.

St. Peter's Square today can be reached from the Ponte Sant'Angelo along the grand approach of the Via della Conciliazione (in honor of the Lateran Treaty of 1929). The spina (median with buildings which divided the two roads of Borgo Vecchio and Borgo nuovo) which once occupied this grand avenue leading to the square was demolished ceremonially by Benito Mussolini himself on October 23, 1936, and was completely demolished by October 8, 1937. St. Peter's Basilica was now freely visible from the Castel Sant'Angelo. After the spina, almost all the buildings south of the passetto were demolished between 1937 and 1950, obliterating one of the most important medieval and renaissance quarters of the city. Moreover, the demolition of the spina canceled the characteristic Baroque surprise, nowadays maintained only for visitors coming from Borgo Santo Spirito. The Via della Conciliazione was completed in time for the Great Jubilee of 1950.

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The Mausoleum of Hadrian, also known as Castel Sant'Angelo is a towering rotunda (cylindrical building) in Parco Adriano, Rome, Italy. It was initially commissioned by the Roman Emperor Hadrian as a mausoleum for himself and his family. The popes later used the building as a fortress and castle, and it is now a museum. The structure was once the tallest building in Rome.

The tomb of the Roman emperor Hadrian, also called Hadrian's mole, was erected on the right bank (or northern edge) of the Tiber, between 134 and 139 CE. Originally the mausoleum was a decorated cylinder, with a garden top and golden quadriga. Hadrian's ashes were placed here a year after his death in Baiae in 138, together with those of his wife Sabina, and his first adopted son, Lucius Aelius, who died in 138. Following this, the remains of succeeding emperors were also placed here, the last recorded deposition being Caracalla in 217. The urns containing these ashes were probably placed in what is now known as the Treasury Room, deep within the building. Hadrian also built the Pons Aelius facing straight onto the mausoleum – it still provides a scenic approach from the center of Rome and the left bank of the Tiber, and is renowned for the Baroque additions of statues of angels holding aloft instruments of the Passion of Christ.

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Ponte Sant'Angelo, originally the Aelian Bridge or Pons Aelius, is a Roman bridge in Rome, Italy, completed in 134 AD by Roman Emperor Hadrian (Publius Aelius Hadrianus), to span the Tiber from the city centre to his newly constructed mausoleum, now the towering Castel Sant'Angelo. The bridge is faced with travertine marble and spans the Tiber with five arches, three of which are Roman; it was approached by means of a ramp from the river. The bridge is now solely pedestrian and provides a scenic view of Castel Sant'Angelo.

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