St Peter’s Basilica Vatican is one of those places that no matter how many times you walk through its vast nave, there’s always something left unnoticed, some detail that didn’t register the first or the other time. On my most recent visit, I gave myself time to simply wander: to circle back, look up, pause, and photograph. I’ve already written about a few specific works inside the Basilica, but until now, never about the building itself. This post is a broader look at its layered history, from the tomb of the Apostle Peter and Constantine’s original basilica, to the Renaissance reconstruction and its present-day role – not just as a church, but as a space shaped by centuries of architecture, ritual, and pilgrimage.

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St Peter’s Basilica is one of those places where, no matter how many times you visit, there is always something new to discover – some detail you missed before. The last time I was there, I gave myself over two, perhaps even three hours just to wander, taking photographs, circling around again and again. I’ve already written a few posts focusing on particular sculptures that caught my attention, each time finding something worth reflecting on. In the meantime, I also had the chance to visit Istanbul, and to step inside Hagia Sophia – so I do have something to compare it with, although admittedly much of Hagia Sophia’s former splendour has not survived. Now, it’s finally time for a proper post dedicated to St Peter’s Basilica itself.

Standing atop the burial place of Saint Peter

St Peter’s Basilica in the Vatican was constructed above the tomb of the Apostle Peter, one of the twelve disciples of Jesus and, according to tradition, the first pope. Peter, a Galilean fisherman, became His disciple and close companion after encountering Jesus. Jesus of Nazareth, a first-century Jewish teacher and preacher, is regarded in Christian tradition as the Messiah and the Son of God. His teachings form the foundation of Catholicism, which has evolved over the centuries, notably through the interpretation of His words and actions within Church tradition.

Saint Peter with the Keys, depicted in mosaic. The keys symbolise the authority given to him by Christ, as recounted in the Gospel of Matthew: “I will give you the keys of the kingdom of heaven” (Mt 16:19).

According to historical accounts, Peter was crucified in Rome around AD 64, during the reign of Emperor Nero, amidst one of the earliest waves of Christian persecution. The immediate backdrop to these events was the Great Fire of Rome. Although the true cause of the fire remains unknown, the Roman historian Tacitus records that Christians were blamed by Nero. Their refusal to participate in imperial and pagan cults was perceived as a threat to public order. Condemned Christians perished in the arenas, in the flames of pyres, and on crosses. According to tradition, Peter requested to be crucified head downwards, believing himself unworthy to die in the same manner as Jesus.

After the execution, Peter’s body was reportedly buried in a cemetery along the Via Cornelia, at the site where the Basilica now stands. In the 20th century, during archaeological excavations beneath the Basilica, a complex of tombs was discovered, which has been identified as the site of Peter’s burial. Today, his grave may be viewed as part of the so-called Scavi Tour, guided visits conducted for small groups by prior reservation. Photography and filming are forbidden benath and appropriate dress is required. The entry is limited to visitors aged 15 and above.

When I visited the Basilica, it was possible to descend into the crypts beneath the church, where numerous papal tombs are located and freely accessible to visitors. However, the entrance to the Vatican Necropolis, where St Peter’s tomb lies, was closed to the public. It could only be viewed through a protective glass panel, offering a limited yet evocative glimpse into one of the most sacred spaces of the Christian world.

The Old and New St Peter’s Basilica

The St Peter’s Basilica we know today was constructed on the site of an earlier church known as Old St Peter’s Basilica, which was erected in the 4th century at the initiative of Emperor Constantine the Great. He was the first Roman emperor to legalise Christianity and to begin establishing public places of Christian worship. In AD 313, he issued the so-called Edict of Milan, which granted freedom of religion and enabled Christian communities to operate without fear of persecution.

Constantine commissioned the construction of a basilica above the tomb of the Apostle Peter – a location that was already recognised as a site of pilgrimage. The Old St Peter’s Basilica followed a traditional longitudinal basilica layout with five aisles – a wide central nave flanked by two narrower aisles on each side, separated by rows of marble columns. At the entrance stood a spacious atrium, known as the Paradise, featuring a central fountain for ritual ablutions, leading into the church through a narthex. The structure had no transept, and its orientation was purely linear, culminating in a large semicircular apse that housed the bishop’s throne and clergy seating. The high altar was positioned directly above the tomb of St Peter, which could be accessed via the confessio, a sunken space that allowed pilgrims to approach the apostle’s grave. Over time, the Basilica was embellished with mosaics, reliquaries, and imperial offerings, transforming it into a richly decorated liturgical and devotional space.

A historical reconstruction of the Old Basilica of St Peter, erected in the 4th century by Emperor Constantine on the site of the Apostle Peter’s tomb. This early Christian basilica stood for over twelve centuries as the liturgical and symbolic heart of Western Christendom. (Image: Wikimedia Commons)

For more than 1,200 years, this structure served as a significant liturgical and symbolic centre of Western Christianity. While Old St Peter’s Basilica became the liturgical heart of Western Christianity, the centre of Eastern Christianity was the Hagia Sophia in Constantinople, also originally commissioned by Emperor Constantine.

The Old Basilica functioned for many centuries as a site of papal liturgies, coronations, and pilgrimages, but over time it fell into serious disrepair, due both to the passage of time and the lack of systematic maintenance. In the second half of the 15th century, discussions began concerning its restoration. However, Pope Julius II, judging the building’s poor structural condition and the evolving liturgical needs of the Church, ultimately decided to demolish it entirely and construct a new church in its place.

This decision was controversial – many believed the historic structure should be preserved. Ultimately, however, the vision of creating a New Basilica reflecting Renaissance ideals of harmony and grandeur prevailed. The demolition of the Old Basilica began gradually, while at the same time foundations were laid for the new one. The tomb of St Peter was never disturbed, and it remained the focal point of the new basilica as well.

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Constructed Over More Than 120 Years

The construction of the new St Peter’s Basilica began on 18 April 1506, at the behest of Pope Julius II, who sought to erect a church that would meet the liturgical and aesthetic demands of the time. The works continued for over 120 years, involving multiple design phases and numerous conceptual changes – reflecting both the development of architectural thought and the succession of different popes.

The first architect entrusted with the project was Donato Bramante, who proposed a centralised plan based on a Greek cross, crowned by a monumental dome at the intersection of the arms. This Greek cross layout, with four arms of equal length, was symbolic of perfect symmetry and balance, reflecting Renaissance ideals and diverging from the traditional Latin cross plan with its elongated nave. After his death, the work was taken up successively by Raphael, Antonio da Sangallo the Younger, and Baldassare Peruzzi, each introducing numerous modifications and new ideas. Despite stylistic differences, they all retained the centralised layout as the foundation of the composition.

A turning point came in 1546, when Michelangelo, then aged 71, assumed supervision of the construction. Although he preserved the overall concept of a centralised plan, he simplified earlier designs and gave the building a more cohesive and monumental character. The most defining feature of his contribution was the dome, the lower section of which was completed during his lifetime. The upper part, along with its crowning lantern, was finished after his death, under the direction of Giacomo della Porta and Domenico Fontana.

In the following decades, the Basilica’s layout underwent a significant transformation. Carlo Maderno, working under Pope Paul V, extended the nave, thereby modifying the original Greek cross plan into a Latin cross. Whereas the Greek cross features arms of equal length, the Latin cross is characterised by a longer vertical axis – a more traditional and longitudinal structure that emphasised processional movement and hierarchical space. Maderno also designed the current façade, completed in 1614, which faces St Peter’s Square. Gian Lorenzo Bernini, involved in the final phase of the project, was responsible for, among other elements, the bronze baldachin above the main altar and the iconic colonnade that embraces the square.

The bronze baldachin created by Bernini stands as one of the most iconic features of the Basilica. However, in keeping with a long-standing Roman tradition, the material used for its construction was reclaimed. To create this monumental work, bronze panels from the ceiling of the Pantheon were stripped and repurposed – an act that, even at the time, sparked controversy and came to symbolise the tensions between preservation and renewal in Baroque Rome.

Distinctive Features of the Basilica

St Peter’s Basilica measures 187 metres in length and 58 metres across the central nave, with a total floor area exceeding 15,000 square metres. Its vast interior can accommodate up to 60,000 people. What sets it apart from other churches is not only its sheer scale, but also its remarkable attention to proportion, light, and materials.

The central nave of St Peter’s Basilica, framed by colossal pilasters and richly decorated with coffered ceilings, leads the eye toward the Papal Altar and the dome.

The dome of the Basilica, designed by Michelangelo, reaches a height of 136 metres from the floor to the cross and is visible from many points across Rome. Its internal diameter measures approximately 42 metres, making it one of the largest domes in the world, comparable in scale to that of the Pantheon. The dome rests upon a massive drum pierced with windows, which allow light to enter and create a sense of vertical rhythm within the space.

The interior of the Basilica’s dome, designed by Michelangelo, is supported by a ring of windows that allow natural light to enter the space. The detailed mosaics and large inscription around the base are clearly visible from below.

The interior of the Basilica does not contain traditional paintings on canvas or plaster. What may appear from a distance to be painted images are, in fact, mosaics, composed of millions of tiny, coloured tesserae arranged with extraordinary precision. These mosaics depict biblical scenes, saints, and ornamental motifs. Their use was also practical: in the damp and often chilly interior, mosaics are more durable than traditional frescoes or oil paintings.

One of many mosaics in the Basilica that resemble painted canvases. The Last Communion of Saint Jerome (1614–1870) is a faithful mosaic reproduction of a work by Domenichino (Domenico Zampieri), a leading painter of the Roman Baroque. The original painting is now displayed in the Vatican Pinacoteca

The entire interior is governed by a strong sense of axial alignment and symmetry. The central nave draws the eye directly towards the Confessio of St Peter – the site traditionally believed to house his tomb. The main altar, surmounted by Bernini’s bronze baldachin, stands precisely above this sacred point. The regular rhythm of columns, coffered ceilings, and niches containing sculptures creates a modular structure, helping visitors navigate the space and lending a measured cadence to the vast interior.

The Basilica’s two most prominent altars – the Papal Altar beneath Bernini’s bronze baldachin and the Altar of the Chair of Saint Peter at the far end of the nave – serve distinct liturgical and symbolic purposes. The Papal Altar, also known as the Altar of the Confession, is located directly above the tomb of Saint Peter, at the crossing of the Basilica’s main axis. It is surmounted by Gian Lorenzo Bernini’s monumental bronze canopy, commissioned by Pope Urban VIII in the 17th century. This altar holds unique status: only the pope may celebrate Mass at it, or a priest explicitly authorised to do so. It is the true liturgical heart of the Basilica, marking the physical and spiritual centre of the Catholic Church. In contrast, the Altar of the Chair, situated in the apse, is a theological and symbolic focal point. It houses the Cathedra Petri – a relic believed to be the wooden throne of Saint Peter – enshrined within Bernini’s baroque sculptural masterpiece, completed in 1666. Though rarely used for liturgical celebrations, this altar embodies the continuity of apostolic succession and the teaching authority of the papacy.

The Altar of the Chair of Saint Peter, located in the apse of the Basilica, features Bernini’s grand sculptural composition framing the symbolic cathedra. Surrounding the throne are dynamic figures of the Doctors of the Church – Ambrose, Augustine, Athanasius, and John Chrysostom – while above them, a radiant alabaster window depicts the Holy Spirit as a dove, casting warm light into the space.

The Basilica’s interior is crafted primarily from marble, sourced from across Italy and the former Roman Empire. Decorative materials also include bronze, gilding, and a variety of precious and semi-precious stones. Many of these elements are spolia, repurposed from the ruins of ancient Roman buildings, lending the structure both material richness and historical continuity.

Despite its dominant sacred function, the Basilica also serves as a museum-like space, housing a wealth of artworks of exceptional historical and artistic value. These include monumental papal tombs and the already mentioned baldachin by Bernini. The result is a complex architectural and artistic ensemble, in which liturgical, symbolic, and touristic functions intertwine on a daily basis.

Artworks from St Peter’s Basilica. From lifelike marble figures to mosaics that appear painted from afar, each piece reveals the Basilica’s unique blend of spiritual meaning and artistic mastery.

It Is Not the Pope’s Cathedral

Although St Peter’s Basilica in the Vatican is the most well-known Catholic church and the site of many major liturgical events, it is not officially the pope’s cathedral. The cathedral of the Bishop of Rome, and thus the principal church of the Diocese of Rome, is the Archbasilica of St John Lateran (Archibasilica Sanctissimi Salvatoris), located in the southeastern part of Rome, outside the boundaries of Vatican City.

It is the Lateran, not the Vatican, that is the oldest papal seat and the true mother church of Catholicism – it even bears the title “Mother and Head of all the Churches in the City and the World”. The Lateran Basilica has served as the cathedral of the Bishop of Rome since the 4th century, and it is there that the cathedra, or episcopal throne, symbolising papal pastoral authority, is found.

In practice, however, the pope most often celebrates liturgy at St Peter’s Basilica, as it is located at the heart of the Vatican, is far larger, more accessible to pilgrims, and closely associated with the figure of St Peter. Nevertheless, in canonical and administrative terms, it is the Lateran Basilica that remains his official cathedral.

This fact often surprises visitors to the Vatican, particularly those from outside Europe, where St Peter’s Basilica is widely assumed to be the pope’s main church and residence. In reality, this is the result of the historical development of the Church’s presence in Rome, and a legacy of the ancient urban structure of the city.

Early Christianity in Rome was centred not in the Vatican, but in the Lateran, where the first official papal complex was built on land donated to the Church by Emperor Constantine. For many centuries, the Lateran served as the administrative and liturgical centre of the Roman Church. Only in the 14th century, after the popes returned from Avignon, did the Vatican gain prominence as the papal residence, and St Peter’s Basilica gradually became the main setting for public ceremonies.

Today, although the papal apartments, the offices of the Roman Curia, and the principal stage for global religious events are all located in the Vatican, the legal status of the cathedral has never changed. It is in the Basilica of St John Lateran that the pope is formally installed as Bishop of Rome, and it is there that the cathedra, the symbolic bishop’s throne, is found. For this reason, Lateran remains the most important church in canonical order.