In Roman Catholic tradition, the basilica is the burial site of its namesake Saint Peter, who was one of the twelve apostles of Jesus and, according to tradition, the first Bishop of Rome and therefore first in the line of the papal succession. Tradition and some historical evidence hold that Saint Peter's tomb is directly below the altar of the basilica.
During Nero’s great Christian persecution in 64 A.D., Saint Peter was martyred, crucified and buried in Caligula’s Circus.
After Constantine’s Edict of Milan (313 A.D.) Christians were allowed to construct places of worship. Constantine himself authorized the building of the basilica in 324. It was intended to allow Peter’s tomb to become the centre of the structure. The great Basilica was consecrated in 329.
By the early 16th century, the need to choose between restoring St Peter’s or rebuilding it completely was unavoidable, so much so that the new Pope Julius II, elected in October 1503, decided to entrust this task to Donato Bramante in 1505, one of the greatest architects of his time.
Construction halted, however, when Julius II (1513) and Bramante (1514) died; by then several other proposals for St Peter’s were drawn up over the next 40 years.
Finally in 1547, Pope Paul III commissioned Michaelangelo to propose a new design.
The building was finished, although the dome was not completed at Michelangelo’s death in 1564. His pupil, Giacomo della Porta, finished building it with a few changes.
At the end of the Council of Trent, in 1563, Carlo Maderno was therefore asked to extend Michelangelo’s original plan.
He added two bays, turning St Peter’s floor plan into a Latin cross. Maderno also designed St Peter’s “classical” façade, built between 1607 and 1612. Unfortunately it tended to hide Michelangelo’s dome and reduce its visual impact. Bernini’s square sought to resolve the problem with an optical effect that draws the dome forward.

The Mausoleum of Hadrian, usually known as the Castel Sant'Angelo, is a towering cylindrical building. It was initially commissioned by the Roman Emperor Hadrian as a mausoleum for himself and his family. The building was later used by the popes as a fortress and castle.
The popes converted the structure into a castle at the beginning of the 14th century; Pope Nicholas III connected the castle to St. Peter's Basilica by a covered fortified corridor called the Passetto di Borgo. The fortress was the refuge of Pope Clement VII from the siege of Charles V's Landsknechte during the Sack of Rome (1527), in which Benvenuto Cellini describes strolling the ramparts and shooting enemy soldiers. Leo X built a chapel with a Madonna by Raffaello da Montelupo. In 1536 Montelupo also created a marble statue of Saint Michael holding his sword after the 590 plague to surmount the Castel. Later Paul III built a rich apartment, to ensure that in any future siege the Pope had an appropriate place to stay. Montelupo?s statue was replaced by a bronze statue of the same subject, executed by the Flemish sculptor Peter Anton von Verschaffelt, in 1753. Verschaffelt's is still in place, though Montelupo's can be seen in an open court in the interior of the Castle. The Papal state also used Sant'Angelo as a prison; Giordano Bruno, for example, was imprisoned there for six years. Executions were made in the small interior square. As a prison, it was also the setting for the third act of Giacomo Puccini's Tosca from whose ramparts the eponymous heroine of the opera leaps to her death.

Navona Square, the most beautiful baroque square in Rome, sits on the ancient ring of the Stadium of Domitian ? also known as Circus Agonalis ? built in 85 AD to host Greek athletic events, agones, with the typical rectangular shape of the arena with its curved northern side.
In the 16th century, the square was enriched with the fountains donated by Pope Gregory XIII Boncompagni; then, Pope Innocent X ordered the construction of the majestic Pamphili Palace on the land owned by his family.
The Square was meant to celebrate the prestige of the Pamphili family, within a sort of competition with the Barberini and Farnese families, so Innocent X ordered the construction of the palace and the decoration of the square with very valuable works. Some pre-existing buildings were pulled down and the main architects of the time fought very hard to get the job.
A very significant role in the selection of the artists was played by the powerful Donna Olimpia Maidalchini, who decided to give the job to Bernini. During the second half of the 17th century, Innocent X ordered the construction of a fountain in the middle of the square, giving the job to Borromini at first. Then, the job was given to Gian Lorenzo Bernini, who enthralled the Pope with a silver model of his fountain.
The Fountain of the Four Rivers (Fontana dei Quattro Fiumi), unveiled in 1651, is definitely one of the most beautiful and famous monuments in baroque Rome and represents the four major rivers known at the time. The Ganges, Nile, Danube and Plate: four white marble, 5-metre high statues located on travertine juts. The Nile, by G.A. Fancelli, has its head draped because its source was unknown at the time. However, the population thought that it expressed Bernini?s contempt for the nearby church of Sant?Agnese in Agone, designed by his rival Borromini, as the Rio de la Plata?s arm raised to protect its head, by Francesco Baratta, ironically expressed the artist?s fear that the church may collapse.
However, these rumours are totally groundless because Bernini finished the fountain before Borromini started the church. Finally, the Ganges is by Claude Poussin, while the Danube is by Antonio Raggi.
After 1870, when Rome became the Capital of Italy, the square was paved with the typical sampietrini and equipped with the central humped pavement: thus, the square became convex.

The Spanish Steps are a set of steps climbing a steep slope between the Piazza di Spagna at the base and Piazza Trinità dei Monti, dominated by the Trinità dei Monti church at the top.The monumental stairway of 138 steps was built with French diplomat Étienne Gueffier?s bequeathed funds of 20,000 scudi, in 1723?1725, linking the Bourbon Spanish Embassy and the Trinità dei Monti church that was under the patronage of the Bourbon kings of France, both located above to the Holy See in Palazzo Monaldeschi located below. The stairway was designed by architects Francesco de Sanctis and Alessandro Specchi.

The Roman Forum (Latin: Forum Romanum, Italian: Foro Romano) is a rectangular forum (plaza) surrounded by the ruins of several important ancient government buildings at the center of the city of Rome. Citizens of the ancient city referred to this space, originally a marketplace, as the Forum Magnum, or simply the Forum. It was for centuries the center of Roman public life: the site of triumphal processions and elections, venue for public speeches, criminal trials, and gladiatorial matches and nucleus of commercial affairs. Here statues and monuments commemorated some of the city's most notable figures. Located in the small valley between the Palatine and Capitoline Hills, the Forum today is a sprawling ruin of architectural fragments and intermittent archeological excavations attracting numerous sightseers. Many of the oldest and most important structures of the ancient city were located on or near the Forum. The Kingdom's earliest shrines and temples were located on the southeastern edge. These included the ancient former royal residence, the Regia (8th century BC), and the Temple of Vesta (7th century BC), as well as the surrounding complex of the Vestal Virgins, all of which were rebuilt after the rise of imperial Rome. Other archaic shrines to the northwest, such as the Umbilicus Urbis and the Vulcanal (Shrine of Vulcan), developed into the Republic's formal Comitium (assembly area). This is where the Senate ? as well as Republican government itself ? began. The Senate House, government offices, tribunals, temples, memorials and statues gradually cluttered the area. Over time the archaic Comitium was replaced by the larger adjacent Forum and the focus of judicial activity moved to the new Basilica Aemilia (179 BC). Some 130 years later, Julius Caesar built the Basilica Julia, along with the new Curia Julia, refocusing both the judicial offices and the Senate itself. This new Forum, in what proved to be its final form, then served as a revitalized city square where the people of Rome could gather for commercial, political, judicial and religious pursuits in ever greater numbers. Eventually much economic and judicial business would transfer away from the Forum Romanum to the larger and more extravagant structures (Trajan's Forum and the Basilica Ulpia) to the north. The reign of Constantine the Great, during which the Empire was divided into its Eastern and Western halves, saw the construction of the last major expansion of the Forum complex ? the Basilica of Maxentius (312 AD). This returned the political center to the Forum until the fall of the Western Roman Empire almost two centuries later.

La Bocca della Verità (in English, "the Mouth of Truth") is an image, carved from Pavonazzetto marble, of a man-like face, located in the portico of the church of Santa Maria in Cosmedin in Rome, Italy. The sculpture is thought to be part of a 1st century ancient Roman fountain, or perhaps a manhole cover, portraying one of several possible pagan gods, probably Oceanus. Most Romans believe that the 'Bocca' represents the ancient god of the river Tiber. The most famous characteristic of the Mouth, however, is its role as a lie detector. Starting from the Middle Ages, it was believed that if one told a lie with one's hand in the mouth of the sculpture, it would be bitten off. The piece was placed in the portico of the Santa Maria in Cosmedin in the 17th century. This church is also home to the supposed relics of Saint Valentine.

The Pantheon was commissioned by Marcus Agrippa as a temple to all the gods of Ancient Rome and rebuilt by Emperor Hadrian in about 126 AD.
In the aftermath of the Battle of Actium (31 BC), Marcus Agrippa built and dedicated the original Pantheon during his third consulship (27 BC).
It had long been thought that the current building was built by Agrippa, with later alterations undertaken, and this was in part because of the inscription on the front of the temple. The inscription across the front of the Pantheon says, M.AGRIPPA.L.F.COS.TERTIUM.FECIT, meaning "Marcus Agrippa, son of Lucius, having been consul three times, built it." However, archaeological excavations have shown that the Pantheon of Agrippa had been completely destroyed except for the facade, and Emperor Hadrian was responsible for rebuilding the Pantheon on the site of Agrippa's original temple.
In 609, the Byzantine emperor Phocas gave the building to Pope Boniface IV, who converted it into a Christian church and consecrated it to Sancta Maria ad Martyres, but informally known as Santa Maria della Rotonda. The square in front of the Pantheon is called Piazza della Rotonda.
Since the Renaissance the Pantheon has been used as a tomb. Among those buried there are the painters Raphael and Annibale Carracci, the composer Arcangelo Corelli, and the architect Baldassare Peruzzi. In the 15th century, the Pantheon was adorned with paintings: The best-known is the Annunciation by Melozzo da Forlì. Architects, like Brunelleschi, who used the Pantheon as help when designing the Cathedral of Florence's dome, looked to the Pantheon as inspiration for their works.
Two kings of Italy are buried in the Pantheon: Vittorio Emanuele II and Umberto I, as well as Umberto's Queen, Margherita. Although Italy has been a republic since 1946, volunteer members of Italian monarchist organisations maintain a vigil over the royal tombs in the Pantheon. This has aroused protests from time to time from republicans, but the Catholic authorities allow the practice to continue, although the Italian Ministry of Cultural Heritage is in charge of the security and maintenance.
The Pantheon is still used as a church. Masses are celebrated there, in particular on important Catholic days of obligation and weddings.

Piazza del Popolo is a large urban square in Rome. The name in modern Italian literally means "People's Square", but historically it derives from the poplars (populus in Latin, pioppo in Italian) after which the church of Santa Maria del Popolo, in the northeast corner of the piazza, takes its name. For centuries, the Piazza del Popolo was a place for public executions, the last of which took place in 1826. The layout of the piazza today was designed in neoclassical style between 1811 and 1822 by the architect Giuseppe Valadier. He removed a modest fountain by Giacomo Della Porta, erected in 1572, and demolished some insignificant buildings and haphazard high screening walls to form two semicircles, reminiscent of Bernini's plan for St. Peter's Square. An Egyptian obelisk of Sety I (later erected by Rameses II) from Heliopolis stands in the centre of the Piazza. Three sides of the obelisk were carved during the reign of Sety I and the fourth side, under Rameses II. The obelisk, known as the obelisco Flaminio or the Popolo Obelisk, was brought to Rome in 10 BC by order of Augustus and originally set up in the Circus Maximus. It was re-erected here in the piazza by the architect-engineer Domenico Fontana in 1589 as part of the urban plan of Sixtus V. Looking from the north, three streets branch out from the piazza into the city, forming the so-called "trident" (il Tridente): the Via del Corso in the centre; the Via del Babuino to the left (opened in 1525 as the Via Paolina) and the Via di Ripetta (opened by Leo X in 1518 as the Via Leonina) to the right. The twin churches (the chiese gemelle) of Santa Maria dei Miracoli (1681) and Santa Maria in Montesanto (1679), begun by Carlo Rainaldi and completed by Bernini and Carlo Fontana, define the junctions of the roads. Close scrutiny of the twin churches reveals that they are not mere copies of one another, as they would have been in a Neoclassical project, but vary in their details, offering variety within their symmetrical balance in Baroque fashion. The central street, now known as the Via del Corso, was the ancient Via Lata and to the north it links with the ancient Roman road, the Via Flaminia, beyond the city gate and southwards, to the Piazza Venezia (formerly the Piazza San Marco), the Capitol and the forum. The Via di Ripetta leads past the Mausoleum of Augustus to the River Tiber, where the Baroque riverside landing called the Porto di Ripetta was located until it was destroyed in the late nineteenth century. The Via del Babuino ("Baboon"), linking to Piazza di Spagna, takes its name from a grotesque sculpture of Silenus that gained the popular name of "the Baboon". To the north of the piazza stands the Porta del Popolo, beyond which lies the Piazzale Flaminio and the start of the Via Flaminia. The gateway was reworked to give its current appearance by Bernini for Pope Alexander VII in 1655, to welcome Queen Christina of Sweden to Rome following her conversion to Roman Catholicism and her abdication.

Campo de' Fiori, a rectangular square near Piazza Navona, translated literally from Italian means "field of flowers". The name was first given during the Middle Ages when the area was actually a meadow. Executions used to be held publicly in Campo de' Fiori. Here, on 17 February 1600, the philosopher Giordano Bruno was burnt alive by the Roman Inquisition because his ideas (such as heliocentrism) were deemed dangerous and all of his work was placed on the Index of Forbidden Books by the Holy Office. In 1887 Ettore Ferrari dedicated a monument to him on the exact spot of his death: he stands defiantly facing the Vatican, reinterpreted in the first days of a reunited Italy as a martyr to freedom of speech. The body of theologian and scientist Marco Antonio de Dominis was also burned in this square, in 1624. The demolition of a block of housing in 1858 enlarged Campo de' Fiori, and since 1869 there has been a vegetable and fish market there every morning. The ancient fountain known as la Terrina (the "soupbowl") that once watered cattle, resited in 1889, now keeps flowers fresh. Its inscription: FA DEL BEN E LASSA DIRE ("Do the good and let them talk") suits the gossipy nature of the marketplace. In the afternoons, local games of football give way to set-ups for outdoor cafés. At night, Campo de' Fiori is a meeting place for young people, both Italian and foreign.

Even today, in a world of skyscrapers, the Colosseum is hugely impressive. It stands as a glorious but troubling monument to Roman imperial power and cruelty. Inside it, behind those serried ranks of arches and columns, Romans for centuries cold-bloodedly killed literally thousands of people whom they saw as criminals, as well as professional fighters and animals.
The Colosseum was started in the aftermath of Nero's extravagance and the rebellion by the Jews in Palestine against Roman rule. Nero, after the great fire at Rome in AD 64, had built a huge pleasure palace for himself (the Golden House) right in the centre of the city. In 68, faced with military uprisings, he committed suicide and the empire was engulfed in civil wars. The eventual winner Vespasian (emperor 69-79) decided to shore up his shaky regime by building an amphitheatre, or pleasure palace for the people, out of the booty from the Jewish War on the site of the lake in the gardens of Nero's palace.
The Colosseum was opened in AD 80 by Vespasian's son and successor, Titus.
Suitably for that great city, it was the largest amphitheatre in the Roman world, capable of holding some 50,000 spectators.

In 19 BC, supposedly with the help of a virgin, Roman technicians located a source of pure water some 13 km (8.1 mi) from the city. This scene is presented on the present fountain's façade. This Aqua Virgo led the water into the Baths of Agrippa. It served Rome for more than four hundred years. The coup de grâce for the urban life of late classical Rome came when the Goth besiegers in 537/38 broke the aqueducts. Medieval Romans were reduced to drawing water from polluted wells and the Tiber River, which was also used as a sewer. The Roman custom of building a handsome fountain at the endpoint of an aqueduct that brought water to Rome was revived in the 15th century, with the Renaissance. In 1453, Pope Nicholas V finished mending the Acqua Vergine aqueduct and built a simple basin, designed by the humanist architect Leon Battista Alberti, to herald the water's arrival. In 1629 Pope Urban VIII, finding the earlier fountain insufficiently dramatic, asked Gian Lorenzo Bernini to sketch possible renovations, but when the Pope died, the project was abandoned. Though Bernini's project was torn down for Salvi's fountain, there are many Bernini touches in the fountain as it was built. In 1730 Pope Clement XII organized a contest in which Nicola Salvi initially lost to Alessandro Galilei - but due to the outcry in Rome over the fact that a Florentine won, Salvi was awarded the commission anyway. Work began in 1732, and the fountain was completed in 1762, long after Clement's death, when Pietro Bracci's Oceanus (god of all water) was set in the central niche. Salvi died in 1751, with his work half-finished, but before he went he made sure a stubborn barber's unsightly sign would not spoil the ensemble, hiding it behind a sculpted vase, called by Romans the asso di coppe, the "Ace of Cups". The Trevi Fountain was finished in 1762 by Giuseppe Pannini, who substituted the present allegories for planned sculptures of Agrippa and "Trivia", the Roman virgin. A traditional legend holds that if visitors throw a coin into the fountain, they are ensured a return to Rome. An estimated 3,000 euros are thrown into the fountain each day.