Editing St. Peter's Basilica (section)

===Dome: successive and final designs===
The dome of St. Peter's rises to a total height of {{convert|136.57|m|ft}} from the floor of the basilica to the top of the external cross. It is the [[List of tallest domes|tallest dome in the world]].{{NoteTag|This claim has recently been made for Yamoussoukro Basilica, the dome of which, modelled on St. Peter's, is lower but has a taller cross.{{Citation needed|date=May 2017}}}} Its internal diameter is {{convert|41.47|m|ft}},<!---NOTE: This is diameter, NOT HEIGHT. Leave it at 41.47.---> slightly smaller than two of the three other huge domes that preceded it, those of the [[Pantheon, Rome|Pantheon]] of [[Ancient Rome]], {{convert|43.3|m|ft}}, and [[Florence Cathedral]] of the [[Renaissance architecture|Early Renaissance]], {{convert|44|m|ft}}. It has a greater diameter by approximately {{convert|30|ft|m}} than Constantinople's [[Hagia Sophia]] church, completed in 537. It was to the domes of the Pantheon and Florence [[duomo]] that the architects of St. Peter's looked for solutions as to how to go about building what was conceived, from the outset, as the greatest dome of [[Christendom]].

====Bramante and Sangallo, 1506 and 1513====
[[File:Caradosso Foppa, View of Saint Peter's (reverse), 1506, NGA 44669.jpg|thumb|upright|1506 medal by [[Cristoforo Foppa]] depicting Bramante's design, including two of the four flanking smaller domes<ref>{{cite book |last1=De la Croix |first1=Horst |last2=Tansey |first2=Richard G. |last3=Kirkpatrick |first3=Diane |title=Gardner's Art Through the Ages |date=1991 |publisher=Thomson/Wadsworth |isbn=0-15-503769-2 |edition=9th |page=[https://archive.org/details/gardnersartthrou00gard/page/641 641] |url-access=registration |url=https://archive.org/details/gardnersartthrou00gard/page/641}}</ref>{{Failed verification|date=April 2025|reason=The reference to page 641 is incorrect to the linked source, which only has 612 total pages, but what appear to be two additional domes on the left and right sides of the image are instead just half-domes at the ends of the transept.}}]]
The dome of the Pantheon stands on a circular wall with no entrances or windows except a single door. The whole building is as high as it is wide. Its dome is constructed in a single shell of [[concrete]], made light by the inclusion of a large amount of the volcanic stones tuff and pumice. The inner surface of the dome is deeply [[coffering|coffered]] which has the effect of creating both vertical and horizontal ribs while lightening the overall load. At the summit is an ocular opening {{convert|8|m|ft}} across which provides light to the interior.<ref name=BF/>

Bramante's plan for the dome of St. Peter's (1506) follows that of the Pantheon very closely, and like that of the Pantheon, was designed to be constructed in [[Tufa]] Concrete for which he had rediscovered a formula. With the exception of the lantern that surmounts it, the profile is very similar, except that in this case, the supporting wall becomes a [[drum (architecture)|drum]] raised high above ground level on four massive piers. The solid wall, as used at the Pantheon, is lightened at St. Peter's by Bramante piercing it with windows and encircling it with a [[peristyle]].

In the case of [[Florence Cathedral]], the desired visual appearance of the pointed dome existed for many years before [[Filippo Brunelleschi|Brunelleschi]] made its construction feasible.{{NoteTag|The dome of Florence Cathedral is depicted in a fresco at [[Santa Maria Novella]] that pre-dates its building by about 100 years.}} Its double-shell construction of bricks locked together in a herringbone pattern (re-introduced from Byzantine architecture), and the gentle upward slope of its eight stone ribs made it possible for the construction to take place without the massive wooden formwork necessary to construct hemispherical arches. While its appearance, with the exception of the details of the lantern, is entirely Gothic, its engineering was highly innovative, and the product of a mind that had studied the huge vaults and remaining dome of Ancient Rome.<ref name=Hartt>{{Harvnb|Hartt|2006}}</ref>

Sangallo's plan (1513), of which a large wooden model still exists, looks to both these predecessors. He realized the value of both the coffering at the Pantheon and the outer stone ribs at Florence Cathedral. He strengthened and extended the peristyle of Bramante into a series of arched and ordered openings around the base, with a second such arcade set back in a tier above the first. In his hands, the rather delicate form of the lantern, based closely on that in Florence, became a massive structure, surrounded by a projecting base, a [[peristyle]] and surmounted by a spire of conic form.<ref name="Fletcher 1996 p=722"/> According to [[James Lees-Milne]] the design was "too eclectic, too pernickety and too tasteless to have been a success".<ref name=JL-M/>

<gallery mode="packed" heights="190">
File:Roma S.Pietro in Vaticano (zzf).jpg|alt=Engraved image in two parts. The left side shows the exterior of the dome, and the right side shows a cross-section. The dome is constructed of a single shell, surrounded at its base by a continuous colonnade and surmounted by a temple-like lantern with a ball and cross on top.|Bramante's dome
File:Roma S.Pietro in Vaticano (zzg).jpg|alt=An engraved picture showing an immensely complex design for the façade, with two ornate towers and a multitude of windows, pilasters and pediments, above which the dome rises looking like a three-tiered wedding cake.|Sangallo's design
File:Speculum Romanae Magnificentiae- Elevation Showing the Exterior of Saint Peter's Basilica from the South as Conceived by Michelagelo (Published in 1569) MET DT203424.jpg|alt=This engraving shows the chancel end of the building much as it was built, except that the dome in this picture is completely semi-circular, not ovoid|The engraving by Stefan du Pérac was published in 1569, five years after the death of Michelangelo.
</gallery>

====Michelangelo and Giacomo della Porta, 1547 and 1585====
[[File:St. Peter's Basilica Rome - 20140808 2350.jpg|thumb|St. Peter's Basilica from [[Castel Sant'Angelo]] showing the dome rising behind Maderno's façade|alt=Photo. The façade is wide and has a row of huge columns rising from the basement to support the cornice. The ribbed, ovoid dome is surmounted by a lantern topped with ball and cross. Its drum is framed by two very much smaller domes.]]
[[File:S. Pietro May 2022-15.jpg|thumb|The dome was brought to completion by Giacomo della Porta and Fontana.|alt= Photo looking up at the dome's interior from below. The dome is decorated at the top with a band of script. Around its base are windows through which the light streams. The decoration is divided by many vertical ribs which are ornamented with golden stars.]]

Michelangelo redesigned the dome in 1547, taking into account all that had gone before. His dome, like that of [[Florence]], is constructed of two shells of brick, the outer one having 16 stone ribs, twice the number at Florence but far fewer than in Sangallo's design. As with the designs of Bramante and Sangallo, the dome is raised from the piers on a drum. The encircling peristyle of Bramante and the arcade of Sangallo are reduced to 16 pairs of Corinthian columns, each of {{convert|15|m|ft}} high which stand proud of the building, connected by an arch. Visually they appear to buttress each of the ribs, but structurally they are probably quite redundant. The reason for this is that the dome is ovoid in shape, rising steeply as does the [[dome]] of Florence Cathedral, and therefore exerting less outward thrust than does a [[Sphere|hemispherical]] dome, such as that of the Pantheon, which, although it is not buttressed, is countered by the downward thrust of heavy masonry which extends above the circling wall.<ref name=BF/><ref name=JL-M/>

The ovoid profile of the dome has been the subject of much speculation and scholarship over the past century. Michelangelo died in 1564, leaving the drum of the dome complete, and Bramante's piers much bulkier than originally designed, each {{convert|18|m|ft}} across. Following his death, the work continued under his assistant [[Giacomo Barozzi da Vignola|Jacopo Barozzi da Vignola]] with [[Giorgio Vasari]] appointed by [[Pope Pius V]] as a watchdog to make sure that Michelangelo's plans were carried out exactly. Despite Vignola's knowledge of Michelangelo's intentions, little happened in this period. In 1585 the energetic [[Pope Sixtus V]] appointed [[Giacomo della Porta]] who was to be assisted by [[Domenico Fontana]]. The five-year reign of Sixtus was to see the building advance at a great rate.<ref name=JL-M/>

Michelangelo left a few drawings, including an early drawing of the dome, and some details. There were also detailed engravings published in 1569 by Stefan du Pérac who claimed that they were the master's final solution. Michelangelo, like Sangallo before him, also left a large wooden model. Giacomo della Porta subsequently altered this model in several ways. The major change restored an earlier design, in which the outer dome appears to rise above, rather than rest directly on the base.<ref>{{cite book |last1=De la Croix |first1=Horst |last2=Tansey |first2=Richard G. |last3=Kirkpatrick |first3=Diane |title=Gardner's Art Through the Ages |date=1991 |publisher=Thomson/Wadsworth |isbn=0-15-503769-2 |edition=9th |page=[https://archive.org/details/gardnersartthrou00gard/page/663 663] |url-access=registration |url=https://archive.org/details/gardnersartthrou00gard/page/663}}</ref> Most of the other changes were of a cosmetic nature, such as the adding of lion's masks over the swags on the drum in honour of Pope Sixtus and adding a circlet of [[finial]]s around the spire at the top of the lantern, as proposed by Sangallo.<ref name=JL-M/>

A drawing by Michelangelo indicates that his early intentions were towards an ovoid dome, rather than a hemispherical one.<ref name=Gardner/>  In an engraving in [[Galasso Alghisi]]' treatise (1563), the dome may be represented as ovoid, but the perspective is ambiguous.<ref>{{Cite book |url=https://books.google.com/books?id=qP5PAAAAcAAJ&q=Alghisi |title=Galassi Alghisii Carpens., apud Alphonsum II. Ferrariae Ducem architecti, opus |archiveurl=https://web.archive.org/web/20230403022925/https://books.google.com/books?id=qP5PAAAAcAAJ&q=Alghisi |archivedate=3 April 2023 |first1=Galasso |last1=Alghisi |first2=Dominicus |last2=Thebaldius |year=1563 |url-status=live}} pp. 44, 147 of Google PDF download.</ref> Stefan du Pérac's engraving (1569) shows a hemispherical dome, but this was perhaps an inaccuracy of the engraver. The profile of the wooden model is more ovoid than that of the engravings, but less so than the finished product. It has been suggested that Michelangelo on his death bed reverted to the more pointed shape. However, Lees-Milne cites Giacomo della Porta as taking full responsibility for the change and as indicating to Pope Sixtus that Michelangelo was lacking in the scientific understanding of which he himself was capable.<ref name=JL-M/>

Helen Gardner suggests that Michelangelo made the change to the hemispherical dome of lower profile in order to establish a balance between the dynamic vertical elements of the encircling giant order of pilasters and a more static and reposeful dome. Gardner also comments, "The sculpturing of architecture [by Michelangelo]&nbsp;... here extends itself up from the ground through the attic stories and moves on into the drum and dome, the whole building being pulled together into a unity from base to summit."<ref name=Gardner/>

It is this sense of the building being sculptured, unified and "pulled together" by the encircling band of the deep cornice that led Eneide Mignacca to conclude that the ovoid profile, seen now in the end product, was an essential part of Michelangelo's first (and last) concept. The sculptor/architect has, figuratively speaking, taken all the previous designs in hand and compressed their contours as if the building were a lump of clay. The dome ''must'' appear to thrust upwards because of the apparent pressure created by flattening the building's angles and restraining its projections.<ref name=Mignacca/> If this explanation is the correct one, then the profile of the dome is not merely a structural solution, as perceived by Giacomo della Porta; it is part of the integrated design solution that is about visual tension and compression. In one sense, Michelangelo's dome may appear to look backward to the Gothic profile of Florence Cathedral and ignore the [[Classicism]] of the Renaissance, but on the other hand, perhaps more than any other building of the 16th century, it prefigures the [[Baroque architecture|architecture of the Baroque]].<ref name=Mignacca/>

====Completion====
Giacomo della Porta and Domenico Fontana brought the dome to completion in 1590, the last year of the reign of [[Sixtus V]]. His successor, [[Gregory XIV]], saw Fontana complete the lantern and had an inscription to the honour of Sixtus V placed around its inner opening. The next pope, [[Clement VIII]], had the cross raised into place, an event which took all day, and was accompanied by the ringing of the bells of all the city's churches. In the arms of the cross are set two lead caskets, one containing a fragment of the [[True Cross]] and a relic of [[St. Andrew]] and the other containing medallions of the Holy Lamb.<ref name=JL-M/>

In the mid-18th century, cracks appeared in the dome, so four iron chains were installed between the two shells to bind it, like the rings that keep a barrel from bursting. As many as ten chains have been installed at various times, the earliest possibly planned by Michelangelo himself as a precaution, as Brunelleschi did at Florence Cathedral.{{Cn|date=June 2023}}

Around the inside of the dome is written, in letters {{convert|1.4|m|ft}} high:

{{blockquote|TV ES PETRVS ET SVPER HANC PETRAM AEDIFICABO ECCLESIAM MEAM ET TIBI DABO CLAVES REGNI CAELORVM<br />("...&nbsp;you are Peter, and on this rock I will build my church.&nbsp;... and I will give you the keys of the kingdom of heaven&nbsp;..." [[Vulgate]], {{bibleverse||Matthew|16:18–19|4}}.)}}

Beneath the lantern is the inscription:

{{blockquote|S. PETRI GLORIAE SIXTVS PP. V. A. M. D. XC. PONTIF. V.<br />(To the glory of St Peter; Sixtus V, pope, in the year 1590, the fifth of his pontificate.)}}

==== Discovery of Michelangelo draft ====

On 7 December 2007, a fragment of a red chalk drawing of a section of the dome of the basilica, almost certainly by the hand of Michelangelo, was discovered in the Vatican archives.<ref name="bbc_sketch" /> The drawing shows a small precisely drafted section of the plan of the entablature above two of the radial columns of the cupola drum. Michelangelo is known to have destroyed thousands of his drawings before his death.<ref>{{Cite web |publisher=[[BBC]] |title=Rare Michelangelo sketch for sale |date=14 October 2005 |url=http://news.bbc.co.uk/2/hi/entertainment/4343488.stm |archiveurl=https://web.archive.org/web/20220926055418/http://news.bbc.co.uk/2/hi/entertainment/4343488.stm |archivedate=26 September 2022 |accessdate=9 February 2008 |url-status=live}}</ref> The rare survival of this example is probably due to its fragmentary state and the fact that detailed mathematical calculations had been made over the top of the drawing.<ref name="bbc_sketch">{{cite news |url=http://news.bbc.co.uk/2/hi/europe/7133116.stm |title=Michelangelo 'last sketch' found |work=BBC News |date=7 December 2007 |access-date=8 December 2007 |archive-date=20 June 2017 |archive-url=https://web.archive.org/web/20170620000116/http://news.bbc.co.uk/2/hi/europe/7133116.stm |url-status=live }}</ref>