The Dome of St Peter's Basilica, Rome

Short answer

• The dome of St Peter's Basilica in Rome is the great cupola that crowns the largest church in Christendom. It was designed by Michelangelo, who took charge of the basilica in 1546 at the age of 71, and it was completed after his death by Giacomo della Porta and Domenico Fontana in 1590, with the lantern finished in 1593.
• The dome rises 133.30 meters from street level to the top of the cross, according to the Vatican's own data page, and 136.57 meters from the basilica floor, the figure most guides quote. Its inner diameter is 41.50 meters. By the floor-to-cross measure it is the tallest dome in the world, though the ancient Pantheon in Rome is wider.
• Inside, the dome is covered with mosaics of 96 figures arranged in six rings, with a Latin inscription from the Gospel of Matthew running around the drum in letters about 2 meters high. Below it stands Bernini's bronze Baldacchino, built between 1624 and 1633 above the tomb of St Peter.
• Visitors can climb to the top, usually given as 551 steps, with a lift covering the first stretch and leaving about 320 steps on foot. The roof terrace and the lantern gallery give the highest viewpoint in Rome, over St Peter's Square, the Vatican, and the city.
• The dome is the symbol of the basilica and of Rome itself, and it became the model for the great domes that followed it, including St Paul's Cathedral in London and the United States Capitol.

What You Are Looking At

The dome of St Peter’s Basilica is the first thing most visitors see of Rome, and the last thing they forget. It rises over the Vatican at the western edge of the city, a gray-green curve of lead above a ring of columns, topped by a lantern, a gilded globe, and a cross. From the Janiculum Hill it looks close enough to touch. From the highway into Rome it appears on the horizon long before anything else. It has been the emblem of the city for more than four hundred years, and it is still the shape people mean when they say “Rome.”

The dome sits at the crossing of the basilica, the point where the long nave meets the transept, directly above the high altar. That position is not an accident. Below the altar, according to a tradition as old as the church itself, lies the tomb of St Peter, the apostle. The dome marks that spot from the outside, the way a spire marks a parish church, and it turns the whole building into a signpost for the tomb. Everything in the basilica is arranged around it: the nave leads the eye toward it, the Baldacchino stands beneath it, and the mosaics inside it look down on the altar.

It is also a building with a complicated authorship. No single person designed it. Bramante drew the first plan. Raphael and Antonio da Sangallo the Younger worked on it after him. Michelangelo redesigned it and gave it the form we see today. Giacomo della Porta and Domenico Fontana built it. Bernini finished the space beneath it. The dome is the work of five generations of architects across nearly a century, and its history is the history of the Renaissance itself, from the confident classicism of 1506 to the drama of the Baroque.

This article follows that history in order, then looks at how the dome is built, what is inside it, how to climb it, and what it has meant for Rome and for the architecture of the world.

The Numbers: How Big Is the Dome

The dome is enormous, and the figures for it are worth stating carefully, because different sources measure it in different ways and give different answers. The Vatican’s own data page for the dome gives the following figures: an internal height of 117.57 meters from the pavement to the vault of the lantern, an external height of 133.30 meters from street level to the summit of the cross, an internal diameter of 41.50 meters, an external diameter of 58.90 meters, and a total weight of about 14,000 tons. The globe on top is 2.50 meters across and weighs 1,862 kilograms. The cross above it is 3.33 meters high.

Most guides quote a taller figure, 136.57 meters, for the height of the dome. Both figures are correct, and they measure different things. The Vatican’s 133.30 meters is measured from street level outside the basilica. The 136.57 meters is measured from the floor of the basilica, which sits a few meters above the street. The difference is the height of the steps and the platform the basilica stands on. When this article says the dome is about 136 meters high, it means the floor-to-cross measure, the one most visitors have in mind when they stand inside and look up.

By that measure, the dome is the tallest dome in the world. The claim needs its qualification stated plainly, because “tallest” depends on what is being measured. The dome of St Peter’s is not the widest. The ancient Pantheon in Rome, completed around 126 AD under the emperor Hadrian, has a dome 43.3 meters across, which is wider than St Peter’s 41.50 meters. The Pantheon is also much lower, a single hemisphere of concrete, while St Peter’s rises on a tall drum and a steep curve. St Peter’s wins on height. The Pantheon wins on width. Both are in Rome, and the comparison is the point: Michelangelo was working in the shadow of the greatest dome the ancient world had built, and he set out to surpass it in height while matching its ambition.

The scale is hard to grasp from the ground, and the basilica itself plays tricks on the eye. The letters of the inscription around the drum are about 2 meters high, taller than a person, and they look like ordinary lettering from the floor. The four piers that carry the dome each have a perimeter of about 71 meters. The Baldacchino beneath the dome is about 29 meters tall, roughly the height of a nine-story building, and it looks modest under the dome. The dome makes everything beneath it look small, including itself: from St Peter’s Square it seems graceful and almost light, and only the climb reveals how massive it really is.

Bramante’s First Plan

The dome begins with a demolition. The first St Peter’s, built in the fourth century under the emperor Constantine, had stood on the Vatican Hill for more than a thousand years. By 1500 it was old, dark, and partly ruinous, and Pope Julius II decided to replace it with a new church that would be the greatest in Christendom. In 1506 he laid the first stone, and he gave the work to Donato Bramante, the architect of the Tempietto in Rome, a small round temple that had already shown what the Renaissance could do with classical forms.

Bramante’s plan was a Greek cross, four equal arms meeting at a central square, with a great dome over the crossing and four smaller domes around it. The idea came from the ancient world: a domed central space, like the Pantheon, enlarged to the scale of a basilica. Bramante imagined the dome as a hemisphere, a perfect half sphere resting on a drum, modeled on the Pantheon and on the dome of Florence Cathedral, which Filippo Brunelleschi had built a century earlier with a double shell of brick and stone.

Bramante died in 1514, with the work barely begun. Four great piers had been raised at the crossing, and little else. The project then passed through the hands of Raphael, who was made architect in 1514, and Antonio da Sangallo the Younger, who drew up a new plan with a heavier, more fortified dome and a long nave. Sangallo built a large wooden model of his design, which still survives in the Vatican, and it shows a dome that is solid and massive, closer to a fortress than to the dome we know. He died in 1546, and the project was in trouble: the piers were thought too weak to carry the dome Sangallo had planned, the money was short, and the design had lost the clarity of Bramante’s first idea.

Michelangelo Takes Over

In 1546, Pope Paul III persuaded Michelangelo to take charge of the building. Michelangelo was 71 years old, the most famous artist in Europe, and he had never built anything on this scale. He accepted, and according to the accounts of his life he worked without pay for the rest of his years, as an act of devotion. He would work on St Peter’s for the remaining eighteen years of his life, and he would never see the dome finished.

His first decision was to go back to Bramante. He restored the Greek-cross plan, simplified it, and strengthened the four piers and the outer walls so that they could carry the weight of a great dome. He also changed the shape of the dome itself. Where Bramante had imagined a hemisphere, Michelangelo designed a dome that was taller and more pointed, with a double shell: an inner shell that carries the structure, and an outer shell, coated in lead, that protects it and gives the dome its profile. A corridor runs between the two shells, lit by rows of small windows, and it is the passage climbers still use today to reach the top.

The double shell was not Michelangelo’s invention. He had studied Brunelleschi’s dome in Florence, which used the same idea, and he borrowed it deliberately. But his version was larger and more daring. He divided the dome into sixteen ribs, twice the number Brunelleschi had used, and sixteen matching segments between them, and he set the whole structure on a drum pierced by sixteen tall windows. The drum is the cylinder of wall between the roof and the dome itself, and its windows are the main source of light inside the dome. The effect from the floor is a ring of light above the inscription, and then the curve of the dome rising into shadow and mosaic.

Michelangelo built a large wooden model of his dome, and it still survives. The model shows a dome that is lower and rounder than the one that was eventually built, closer to a hemisphere. Whether the final, steeper profile was Michelangelo’s own late revision or his successor’s change is a question historians still debate. What is certain is that Michelangelo designed the dome, fixed its diameter and its double-shell construction, and built the drum. When he died in 1564, at the age of 88, the work had reached the top of the drum and stopped. The cupola itself did not yet exist.

Della Porta and Fontana Finish the Work

For more than twenty years after Michelangelo’s death, the dome stood unfinished. Then Pope Sixtus V, who became pope in 1585 and was a pope in a hurry who was rebuilding Rome at a furious pace, ordered the work resumed and put it in the hands of Giacomo della Porta, assisted by the engineer Domenico Fontana. Della Porta was a pupil of Michelangelo and had worked on the basilica for years. He took Michelangelo’s design and made one decisive change: he raised the profile of the dome, making it steeper and more pointed than the model showed. The change made the dome stronger as well as taller, because a steeper curve pushes less hard against its supports, and it gave the dome the elegant, soaring outline that defines the Roman skyline.

The building went fast. Construction of the vault began in 1588, and the dome was completed in May 1590, in about twenty-two months, with a workforce reported at as many as 800 laborers working in shifts around the clock. The speed was a feat of organization as much as of engineering: brick, stone, and timber had to be lifted hundreds of feet in the air, and the work could not stop for weather or for the services below. Sixtus V died in August 1590, three months after the vault was finished, and the dome stands as his monument as much as Michelangelo’s.

The lantern followed. The small temple-like structure that crowns the dome, with its columns and its gilded globe and cross, was finished on 18 November 1593. The globe and the cross were the work of Sebastiano Torregiano, and the lantern’s completion marked the end of the dome’s construction, forty-seven years after Michelangelo had taken charge. The inscription at the base of the lantern records the fact in Latin: to the glory of St Peter, Pope Sixtus V, in the year 1590, the fifth of his pontificate.

Two details of the finished dome are worth noting. The first is that the dome was built almost exactly to Michelangelo’s plan in its dimensions, even though its profile was changed. The diameter, the double shell, and the sixteen ribs are his. The second is that della Porta’s steeper profile is the reason the dome looks the way it does from a distance: a hemisphere would have looked squat on so tall a drum, and the pointed curve gives the dome its lift. The dome we see is a collaboration, and the collaboration is the point.

Bernini and the Basilica Below the Dome

The dome was finished in 1590, but the basilica was not. Carlo Maderno lengthened the nave and built the facade in the early 1600s, turning Michelangelo’s central plan into a long Latin cross, and the basilica was finally consecrated in 1626, a hundred and twenty years after the first stone was laid. The facade pushed the dome back from the square, so that it is partly hidden from the front, and it is one of the reasons the best view of the dome is from the side, from the gardens, or from the top of the climb.

The interior beneath the dome was Gian Lorenzo Bernini’s work. Bernini was twenty-five when Pope Urban VIII commissioned him in 1624 to build the Baldacchino, the great bronze canopy over the papal altar. He took nine years to make it, from 1624 to 1633, and it was his first work in the basilica. The Baldacchino stands on four marble pedestals, and its four twisted bronze columns rise about 20 meters, carrying a canopy that reaches about 29 meters in all. The bronze came in part from the Pantheon, whose ancient bronze roof beams were melted down for the purpose, a fact that Romans noted with disapproval at the time. The columns are decorated with olive and bay branches, cherubs, and the bees of the Barberini family, the family of Urban VIII, and the whole structure is a piece of theater: a tent of bronze that marks the tomb below and draws the eye upward to the dome.

Bernini’s work did not stop there. He directed the decoration of the four piers with statues of the saints, carving St Longinus himself, while Francesco Mochi carved St Veronica, François Duquesnoy carved St Andrew, and Andrea Bolgi carved St Helena. He designed the Cathedra, the great bronze throne at the far end of the basilica, and in the 1650s and 1660s he built the colonnade that embraces St Peter’s Square, the great curved arms of columns that turn the square into an open-air church. The colonnade is the frame for the dome, and the dome is the crown of the whole composition. Bernini understood the dome as the center of a system, not as an isolated object, and his work beneath it and around it is what makes the dome feel like the heart of the basilica rather than its roof.

How the Dome Stands Up

A dome of this size should not stand up. Masonry is strong in compression, when it is squeezed, and weak in tension, when it is pulled apart, and a dome works by squeezing its stones together in rings. The problem is at the base, where the curve pushes outward against the walls, a force engineers call thrust. If the thrust is not contained, the dome spreads, cracks open, and falls. St Peter’s dome is a lesson in how Renaissance builders contained that force, and in how close they came to failing.

The first answer was the double shell. The inner shell is thick and structural, and it carries the weight. The outer shell is thinner and lighter, and it protects the inner shell from the weather and gives the dome its profile. Between the two shells runs the corridor that climbers use, and the air in the corridor helps the structure breathe. The second answer was the drum, which is itself a massive ring of travertine, and the sixteen ribs that run up the dome and concentrate its weight onto the piers. The third answer was the piers themselves, four enormous masses of masonry that anchor the whole structure to the ground.

The fourth answer was iron. Michelangelo’s design specified three iron chains to bind the masonry the way hoops bind a barrel, and iron chains were built into the dome during construction. Counts in the sources vary: the Getty records four iron chains in the compression ring. They were not enough. Cracks began to appear in the dome not long after it was finished, and by the early eighteenth century they were wide enough to alarm the popes. In 1742, Pope Benedict XIV appointed three mathematicians, Roger Joseph Boscovich, Francois Jacquier, and Thomas Le Seur, to inspect the dome and report on its safety. They climbed through the dome, mapped the cracks, and reported that the structure was no longer a single solid mass but a series of arches held together at the top, and that it needed reinforcement.

The Venetian physicist Giovanni Poleni was then asked to study the problem. He divided the dome into fifty arches in his analysis and showed, using the mathematics of the hanging chain, that the line of thrust still fell within the thickness of the masonry, which meant the dome was stable but needed help. Between 1743 and 1747, under the architect Luigi Vanvitelli, five great iron hoops were fitted around the dome, at levels from the drum to near the lantern, each one made of bars lifted by hand to the roof terrace and joined into a continuous ring. The work was finished in the late 1740s, and the dome has stood secure ever since. The hoops are still there, hidden under the lead, and they are the reason the dome survives: a piece of eighteenth-century engineering holding up a sixteenth-century design.

A lightning rod was added to the dome in 1809, under the direction of Bishop Luigi Filippo Gilj, after lightning had repeatedly struck the lantern. The dome has been struck many times since, and the rod has done its work. The building is maintained today by the Fabbrica di San Pietro, the Vatican office that has looked after the basilica since the sixteenth century, and its restorers continue to monitor the cracks and the ironwork.

Inside the Dome: Mosaics, Letters, and Light

The inside of the dome is a different world from the outside. From the floor of the basilica, the dome seems impossibly far away, a blue vault scattered with gold figures, lit by the ring of windows in the drum. The decoration is all mosaic, not painting, and it was made to last: small pieces of colored glass and stone set in stucco, which catch the light and glow where paint would have darkened and flaked.

The decoration is divided by the sixteen ribs into sixteen segments, and within those segments the figures are arranged in six ascending rings, one above another, rising from the drum to the lantern. At the bottom, nearest the viewer, stand the first sixteen canonized popes, the early bishops of Rome. Above them come the apostles, the evangelists, and the saints, and at the top, against a deep blue sky scattered with stars, are the angels. In all there are 96 figures, each one larger than life, and each one designed to be read from far below. The figures at the bottom are about life size in the sense that they look life size from the floor; in fact they are far larger, and their faces are simplified so that they can be seen from more than a hundred meters away.

The work took decades and many hands. The decoration of the dome began in the 1590s under Giovanni Guerra, Cesare Nebbia, and Marcantonio Bosco, and in 1597 Pope Clement VIII commissioned Cristoforo Roncalli to design the angels for the pendentives, the curved triangular spaces where the dome meets its supporting arches. The upper part of the decoration was entrusted to Giuseppe Cesari, known as Cavalier d’Arpino, who prepared the designs between 1603 and 1612. His cartoons, full-size drawings in tempera, were then translated into mosaic by the best mosaic artists of the day, working under the direction of Marcello Provenzale, and the work continued into the reign of Pope Paul V. The dome’s mosaics are therefore the work of a generation, not a single artist, and they belong to the Mannerist style of the years around 1600: elegant, elongated figures, rich color, and a composition that is orderly from a distance and full of detail up close.

Around the base of the drum runs the inscription that gives the dome its meaning. In letters about 2 meters high, in black on a gold ground, lit by the sixteen windows, it reads in Latin: “Tu es Petrus et super hanc petram aedificabo ecclesiam meam et tibi dabo claves regni caelorum.” In English: “You are Peter, and upon this rock I will build my church, and to you I will give the keys of the kingdom of heaven.” The words are from the Gospel of Matthew, chapter 16, verses 18 and 19, and they are the foundation of the papacy: Peter as the rock, and the church built on him. The letters were painted between 1605 and 1606, and the gold and blue were applied by Piero Pomodoro. Climbers on the interior walkway pass just above the inscription, close enough to see the size of the letters and the gold behind them.

In the four pendentives, the curved spaces that link the square piers to the circular drum, are medallions of the four Evangelists, each about 8.5 meters across: Matthew with the angel, Mark with the lion, Luke with the ox, and John with the eagle. They are the largest single images in the dome, and they are the first thing a climber sees at close range from the interior walkway. The whole interior is a theological statement made in mosaic: the apostles and the saints below, the angels above, the words of Christ around the drum, and the lantern at the top, where the light comes in. The dome is a picture of heaven, built over the tomb of the apostle.

Climbing the Dome

The dome can be climbed, and it is the best thing to do in the basilica after seeing the interior itself. The climb is the only way to understand the scale of the building, to see the mosaics at close range, and to stand on the highest viewpoint in Rome. It is also a serious climb, and it is worth knowing what it involves before starting.

The climb is usually given as 551 steps from the ground to the top. There is a lift for the first stretch, which carries visitors up to the roof terrace at the base of the dome, and from there the climb continues on foot for about 320 steps. The all-stairs route is 551 steps in total. The Vatican’s own data page lists 537 steps to the summit, so sources differ by a handful of steps, and the exact count depends on where the counting starts. Either way, it is a long climb, and the last section is the hard part: a narrow passage between the inner and outer shells of the dome, where the corridor leans inward with the curve of the dome, and then a tight spiral staircase of marble up to the lantern.

The climb has three stages, and each one is different. The first stage, whether by lift or by stairs, brings you to the roof terrace, a broad flat roof at the base of the dome, with a view over St Peter’s Square and Bernini’s colonnade, and with the smaller domes of the basilica close at hand. The terrace is a good place to rest and to look at the dome from outside at close range, where the ribs, the lead plates, and the buttresses can be seen properly for the first time.

The second stage is the interior walkway, a narrow balcony that runs around the inside of the dome just above the great inscription. From here the mosaics are close enough to touch, or nearly so, and the scale of the figures becomes clear: faces that looked small from the floor are taller than a person. The walkway also gives the best view down into the basilica, to the Baldacchino far below, and the best sense of the height of the interior, 117.57 meters from the floor to the vault of the lantern.

The third stage is the passage between the shells, the corridor Michelangelo built into the dome, lit by small dormer windows. The corridor narrows as it rises, and the wall leans inward, so that near the top you are walking on a slope with a rope for a handrail. Then comes the spiral staircase to the lantern, and then the small gallery around the lantern itself, an open-air balcony at the top of the dome, with a view in every direction.

The view from the top is the reward. To the east lies St Peter’s Square and the long axis of Rome, with the Tiber and the hills beyond. To the south are the Vatican Gardens, open only by guided tour but visible in full from above. To the west and north is the modern city, spreading to the horizon. On a clear day the view runs to the Alban Hills and the sea. It is the highest viewpoint in Rome, and it is the only place from which the whole plan of the basilica, the square, and the Vatican can be seen at once.

A few practical notes belong here. Entry to the basilica itself is free, but the dome climb is ticketed separately, and the ticket is bought at the basilica. The climb is not suitable for everyone: the passages are narrow, the stairs are steep, and the final section is enclosed and sloping, so anyone with claustrophobia, heart problems, or difficulty with stairs should think carefully before starting. Opening hours change with the season, and the dome can close in bad weather, so check the basilica’s official site before you go. If you are planning a wider trip, our day trips from Rome guide covers the places to pair with the Vatican, and our guide to where to stay in Rome covers the neighborhoods to base yourself in.

What the Dome Means for the Basilica and for Rome

The dome is the reason St Peter’s looks the way it does, and it is the reason the basilica matters the way it does. Without the dome, St Peter’s would be a very large church. With it, the building is a landmark that can be seen from every hill in Rome, and a symbol that is recognized everywhere in the world. The dome does three things at once: it marks the tomb of St Peter, it crowns the largest church in Christendom, and it stands for the papacy itself. That is a great deal of meaning for one structure to carry, and it is the reason the dome was built at such cost and with such care.

It is also the reason the dome became a model. St Peter’s dome was completed a century and a half after Brunelleschi’s dome in Florence, and architects across Europe studied it. Its double shell, its drum, its lantern, and its steep profile were copied and adapted for centuries. St Paul’s Cathedral in London, built after the Great Fire of 1666, owes its dome to St Peter’s, and so does the United States Capitol in Washington, whose cast-iron dome is a nineteenth-century descendant of Michelangelo’s design. The dome became the standard form for a great public building, and it still is: a dome on a drum, with a lantern on top, means importance, and it means it because St Peter’s did it best.

The dome also shaped Rome itself. A long-standing rule keeps no building in central Rome taller than the dome, so the skyline of the historic center is low and the dome stands above it, visible from every quarter. The rule is a matter of planning and custom rather than a single law, and modern buildings outside the center are taller, but within the historic city the dome still rules the skyline. The effect is that Rome has no rival to the dome, no tower or skyscraper to compete with it, and the city reads as a flat sea of roofs with one great curve rising from it.

The dome belongs to the same world of power and stone as the castles of Europe. Like the famous castles in Europe, it was built to impress as much as to shelter, and to announce who was in charge before a visitor heard a single word. Readers who like their history in stone may also enjoy our guide to the oldest castle in the world. And St Peter’s itself is regularly named among the most famous buildings in the world, a list in which the dome is the feature that makes the building recognizable.

Four hundred years after it was finished, the dome is still doing the work it was built to do. It still marks the tomb. It still crowns the basilica. It still defines the skyline. And it still draws people up its stairs, to stand on the roof of the Vatican and look out over the city that built it. That is the measure of the building: not its height or its weight, but the fact that it still works, as a church, as a symbol, and as a place to climb, after four centuries.

FAQ

Who designed the dome of St Peter’s Basilica?

Michelangelo designed the dome. He took charge of the basilica in 1546, returned to Bramante’s Greek-cross plan, and designed a double-shell dome with sixteen ribs on a drum with sixteen windows. He died in 1564 with the work finished only to the top of the drum. Giacomo della Porta and Domenico Fontana completed the dome in 1590, raising its profile to the steeper curve we see today, and the lantern was finished in 1593.

How tall is the dome of St Peter’s?

The Vatican’s data page gives 133.30 meters from street level to the top of the cross, and 136.57 meters from the basilica floor, the figure most guides quote. The internal height, from the pavement to the vault of the lantern, is 117.57 meters, and the internal diameter is 41.50 meters. By the floor-to-cross measure it is the tallest dome in the world, though the Pantheon in Rome, at 43.3 meters across, is wider.

How many steps are there to the top of the dome?

The climb is usually given as 551 steps from the ground to the top. A lift covers the first stretch to the roof terrace, leaving about 320 steps on foot. The Vatican’s own data page lists 537 steps to the summit, so sources differ slightly. The final section is a narrow, sloping passage between the dome’s two shells, followed by a spiral staircase to the lantern.

Can you climb to the top of St Peter’s dome?

Yes. The dome climb is open to visitors, with a ticket bought separately from entry to the basilica, which is free. The climb is not suitable for everyone: the passages are narrow and steep, the final section is enclosed and sloping, and anyone with claustrophobia, heart problems, or difficulty with stairs should consider it carefully. Opening hours change with the season, so check the basilica’s official site before you go.

What is inside the dome of St Peter’s?

The interior is covered with mosaics: 96 figures arranged in six rings, from the early popes at the bottom to the angels at the top, against a blue sky scattered with stars. Around the base of the drum runs a Latin inscription from the Gospel of Matthew, chapter 16, in letters about 2 meters high: “You are Peter, and upon this rock I will build my church.” In the four pendentives are medallions of the four Evangelists. Below the dome stands Bernini’s bronze Baldacchino, built between 1624 and 1633 above the tomb of St Peter.

Why is the dome of St Peter’s famous?

It is the tallest dome in the world by the usual measure, and the model for the great domes that followed it, including St Paul’s Cathedral in London and the United States Capitol. It crowns the largest church in Christendom, marks the tomb of St Peter, and defines the skyline of Rome, where a long-standing rule of planning and custom keeps no building in the historic center taller than the dome. It is also, with the climb to its lantern, the highest viewpoint in the city.

Sources & references

• Vatican, "Dome and Lantern", vatican.va. Dimensions (internal height 117.57 m, external height 133.30 m, internal diameter 41.50 m, external diameter 58.90 m, weight 14,000 t, 537 steps, globe and cross dimensions), authorship (Michelangelo, Giacomo della Porta, Domenico Fontana), dates 1546-1593, vault completed May 1590, lantern completed 18 November 1593, double vault construction, corridor between the shells, lightning rod installed 1809.
• St Peter's Basilica guide, "St. Peter's - The Dome", stpetersbasilica.info. Four piers (perimeter 71 m), the inscription text and its source in Matthew 16:18, letters 2 m high, 16 windows in the drum, 16 ribs and 16 segments, 96 figures in six levels, the Evangelists in the pendentives (medallions 8.5 m), Cavalier d'Arpino cartoons 1603-1612, work of Guerra, Nebbia, and Bosco from 1593, inscription letters painted 1605-1606, lantern inscription to Sixtus V.
• St Peter's Basilica guide, "St. Peter's - Papal Altar & Baldacchino", stpetersbasilica.info. Bernini's Baldacchino 1624-1633, four twisted columns 20 m high, whole height 29 m, commissioned by Urban VIII, revealed to the public on St Peter's day 1633; Wittkower, Bernini (1997), whole height 28.5 m.
• Google Arts & Culture, Cristoforo Roncalli, "Three Studies of Angels for a Pendentive". Clement VIII commissioned the mosaic decoration of the dome interior in 1597, choosing Roncalli for the angels beside the four Evangelists in the pendentives.
• Ancient Origins, "The Amazing Altarpieces of St. Peter's Basilica". Mosaic decoration of the great dome 1603-1612, Gregory XIII's decision to use mosaic, the Vatican Mosaic Studio, 28,000 colors of tesserae in the basilica's altarpieces.
• The American Scholar, "Chain Gang", review of Wayne Kalayjian, Saving Michelangelo's Dome. The 1742 inspection by Boscovich, Jacquier, and Le Seur, Poleni's analysis, the iron chains and hoops fitted under Vanvitelli, and the rule that no building in Rome's city center may exceed the height of St Peter's.
• Easy Reader News, "Michelangelo's dome in Rome: catastrophe avoided", interview with Wayne Kalayjian. The dome built 1588-1590, the 1742-1743 report, the five iron hoops installed in 1743-1744, the first hoop 570 feet long and nine tons.
• Hagia Sophia comparison, hagia-sofia.com, "Comparing the domes of Hagia Sophia to the Pantheon and St. Peter's Basilica". Pantheon dome 43.3 m in diameter, completed around 126 AD under Hadrian; St Peter's dome as the model for St Paul's Cathedral and the United States Capitol.
• Lions in the Piazza, "The Pantheon and the Domes of Rome". Michelangelo's doubling of the ribs from eight to sixteen, the double-shell design borrowed from Brunelleschi, St Peter's dome as the template for Western domes.
• Walks of Italy, "Guide to climbing the dome of St. Peter's Basilica". 551 steps in total, 231 steps to the first level, 320 steps to the top, 96 mosaic figures, the lowest ring the first sixteen canonized popes.
• Rome Explored, "St. Peter's Basilica". Construction begun 1506 under Julius II, Michelangelo taking charge in 1547, dome completed 1588-1590 in 22 months with as many as 800 laborers, basilica consecrated 1626, nave floor markers showing St Peter's longer than every other great church.