The basilica of San Petronio is by far the largest church in all of Bologna, and also one of the largest in Italy. The building is 132 metres deep and 60 metres wide. The façade reaches a height of 51 metres and inside the vaults are at least 44 metres high. And yet, the building could have been much, much larger if all the rather megalomanic plans that have been made in the past had actually been put into practice. It immediately becomes clear that several plans were ditched when we study the façade of the San Petronio. Its lower part is decorated with pink and white marble and the three entrances have beautifully decorated portals, but the upper part features just naked brick and holes that could have been (but were not) used for attaching pieces of marble. The façade was evidently never completed. To add insult to injury, the marble decorations are asymmetrical: on the left they are higher than on the right.
In spite of these peculiarities, the San Petronio is still a fascinating church which one simply cannot skip during a stay in Bologna. A visit to the basilica is free, but there is a small catch. If you want to take pictures, you will have to buy a paper bracelet for two Euros and then wear it so the custodians can see you have paid. The money is spent on church maintenance. There is furthermore an admission charge for visits to the famous Chapel of the Magi or Cappella Bolognini. In this chapel photography is regretfully prohibited altogether, whether you have a bracelet or not. The wonderful frescoes on the walls by Giovanni da Modena (ca. 1379-1455) can fortunately also be admired fairly well from the nave of the basilica and there is no ban on taking pictures there.
Saint Petronius was bishop of Bologna, i.e. Roman Bononia, between ca. 431 and 450. After he had died, his role in the religious life of the city was initially not that prominent, but this all changed when, in 1141, his remains were rediscovered in the complex of Santo Stefano elsewhere in Bologna. In the mid-thirteenth century Petronius became patron saint of the city and at the end of 1388 the municipal authorities, i.e. the Council of 600, took the decision to build a Gothic-style church dedicated to him. It is important to note that this decision was taken by the civil authorities, not by the diocese. As a consequence, the San Petronio has been the church of the comune until 1929 and was only transferred to the diocese in that year. This fact also explains why the formal consecration of the church took place as late as 1954. The San Petronio is not, and has never been, the cathedral of Bologna. The actual cathedral, dedicated to Saint Peter, stands about 350 metres north of the San Petronio and is usually ignored by tourists and travel guides alike.
The foundation stone for the basilica was laid on 7 June 1390. The first architect was Antonio di Vincenzo (ca. 1350-1401/02), who was assisted by Andrea da Faenza (1319-1396), a man who was not just the leader of the Servite Order in Bologna, but also an accomplished master builder (see Bologna: Santa Maria dei Servi). Before the construction of the church could start, a whole residential block south of the Piazza Maggiore had to be demolished. Ancient customs dictated that basilicas were properly ‘oriented’, but the San Petronio faces the south instead of the east. The church was built front to back, starting at the façade and ending at the apse, which was fairly uncommon as well. Before he died in 1401 or 1402, Antonio di Vincenzo presumably managed to finish the first two bays, including the chapels. Then there was a delay, for which cardinal Baldassarre Cossa is often blamed. In 1403 this former student at the university of Bologna had been appointed papal legate in Bologna and the Romagna. In 1410 he was even elected antipope John XXIII. Cossa was accused of having confiscated and sold certain building materials that had been intended for the San Petronio project. It is difficult to say whether the accusations were true or simply fabricated. We do know antipope John XXIII had a lot of enemies.
In any case, work was continued in about 1441. In 1462 the third, fourth and fifth bay were complete. Then in 1481-1492 the architect Giovanni da Brensa built the bell-tower of the church. It reaches a height of about 65 metres and can be viewed very well from the Asinelli tower, which is 97 metres high (see the image above). This tower offers a splendid view of the entire basilica, which looks a lot like a giant ark moored against the Piazza Maggiore. As was already mentioned, the ark could have been even larger and more impressive, but in the sixteenth century construction came to a standstill. In 1514 one Arduino Arriguzzi (died 1531) was hired to build a dome, but he failed miserably. Then in 1562 Pope Pius IV (1559-1565) commissioned the Archiginnasio di Bologna, the seat of the university board. The Archiginnasio was built right next to the basilica and blocked the space where the transept of the San Petronio had been planned. And so the basilica ended up in the shape of a classical Roman basilica, without a dome and without a transept.
Due to all the discussion, it was not until the seventeenth century that construction of the San Petronio was continued. The Roman architect Girolamo Rainaldi (1570-1655) was commissioned to design the vaults, but the actual construction of these vaults did not start until some twenty years later, under the direction of the rather obscure Francesco Martini. In 1663 the sixth and final bay and the present apse of the church were completed. After 273 years the basilica of San Petronio was finally finished. However, the only semi-completed façade was a thorn in the side for some, and in 1887 a contest was organised to have it fully decorated after all. The year does not seem to have been randomly picked, as 1887 also saw the completion of the Neogothic façade of the Duomo in Florence. The contest in Bologna was not followed up, however, and the façade remained as it was. In 2000 the relics of Petronius were translated from the complex of Santo Stefano to the basilica dedicated to him. The San Petronio apparently already possessed his head, so that after all these centuries, the saint’s body is now complete again.
Decoration of the façade started when Antonio di Vincenzo was still in charge of the project. The plinth at the bottom, made of pink marble, features several quadrilobes (clover-shaped medallions) from 1393-1394 with eight busts of male saints. According to the website of the basilica these are Saints Franciscus of Assisi, Dominicus, Florianus, Peter, Paul, Ambrosius, Augustinus and of course Petronius. What is interesting is that a German sculptor named Giovanni Ferrabech or Hans von Fernach was involved in the project. The bust of Saint Paul is attributed to him.
The most famous element of the façade is the central portal. Jacopo della Quercia (ca. 1374-1438) from Siena worked on this portal, also known as the Porta Magna, from 1425 until shortly before his death. On either side of the entrance we see ten reliefs depicting Old Testament stories, more specifically from the book of Genesis. The stories about Adam and Eve, Cain and Abel, Noah, Abraham and Isaac are all well known, but they were superbly executed. Above the entrance are five reliefs with stories from the New Testament. We see the Nativity, the Adoration of the Magi, the Presentation in the Temple, the Murder of the Innocent Children and the Flight to Egypt. In the lunette above the reliefs are three statues, representing the Madonna and Child flanked by Saints Ambrosius and Petronius (both bishops). The latter is recognisable by his attribute, a miniature model of the city of Bologna.
The two side portals were made at a later date. They were designed by the architect Ercole Seccadenari (died 1540), who hired many talented artists to make the decorations. While designing the portals, Seccadenari – a scion of a noble Bolognese family – consciously tried to imitate Jacopo della Quercia’s style. He too chose reliefs featuring Old and New Testament scenes and had statues placed inside the two lunettes. On the left we see a sculpture group of the risen Christ between the soldiers by Alfonso Lombardi (ca. 1497-1537), on the right a sculpture group of Christ taken from the cross between the Virgin Mary and Saint John the Evangelist. Christ, and Joseph of Arimathea behind him, were made by Amico Aspertini (ca. 1474-1552), the statue of the Virgin is by Niccolò Tribolo (ca. 1500-1550) and that of John by Ercole Seccadenari himself.
The main entrance once featured a bronze statue of Pope Julius II (1503-1513). It was made – reluctantly, and after a failed casting attempt – by the great artist Michelangelo (1475-1564). The statue was at least four metres high and weighed several thousand kilos. Unfortunately it has not survived. Julius and the city of Bologna did not get along well. Between 1463 and 1506 the city had been ruled by Giovanni II Bentivoglio, but he had been expelled by Julius’ army. On 21 February the Pope had the bronze statue set up above the entrance to the San Petronio. He then appointed his favourite cardinal Francesco Alidosi papal legate of the city. Alidosi, however, was deeply hated by the people and needed continued support from Julius to stay in power. In 1511 Bologna was taken by a French army commanded by the Milanese general Gian Giacomo Trivulzio (ca. 1440-1518). The cardinal fled the city and was subsequently murdered in Ravenna by his old enemy the duke of Urbino. Meanwhile, the citizens of Bologna celebrated. They toppled Julius’ statue and sold the pieces to Alfonso d’Este, duke of Ferrara. Alfonso used the bronze to cast a large canon, which he christened ‘Julius’ or La Giulia. It goes without saying that the relationship between Alfonso d’Este and the Pope was troubled as well.
The interior of the San Petronio is very impressive. A lot of natural light enters the basilica thanks to the large round windows of the clerestory, the aisles and the chapels. Additionally these chapels have high Gothic windows. Stairs at the end of the nave lead to a high altar which stands underneath a baldachin designed by Giacomo Barozzi da Vignola (1507-1573). The dome topping the baldachin was made by the aforementioned Francesco Martini. Above the high altar is a splendid wooden crucifix from the fifteenth century, crafted by an unknown artist. The wooden choir stalls, also fifteenth-century, are of great interest as well. These were made by Agostino de’ Marchi. The big fresco in the apse depicts the Madonna and Child with Saint Petronius and dates from 1672. Carlo Cignani (1628-1719), Marcantonio Franceschini (1648-1729), Luigi Quaini (1643-1717) and Giacomo Alboresi (1632-1677) were all involved in its design and creation.
The San Petronio has a total of 22 chapels, eleven on either side. Some are more interesting than others, and a few are genuine gems. The first chapel on the right is the Cappella di Sant’Abbondio, dedicated to Saint Abundius, a bishop of Como from the fifth century. It is said that, on 24 February 1530, Charles V put on his mantle in this chapel before being crowned and anointed Holy Roman emperor at the high altar by Pope Paus Clemens VII (1523-1534). Imperial coronations obviously used to take place in Saint Peter’s Basilica in Rome, but in May of 1527 Charles’ forces had looted the Eternal City during the notorious Sacco di Roma. Pope Clemens had fled to the Castel Sant’Angelo and then surrendered after a brief siege. As Rome lay in ruins, it was ruled out as a location for Charles’ coronation. Rich Bologna, on the other hand, famed for its university, was a perfect alternative. The interior of the Cappella di Sant’Abbondio was completely remodelled in 1865. The walls do still feature a number of older frescoes by Giovanni da Modena.
The second chapel on the left is the Cappella di San Petronio, dedicated to Bologna’s patron saint. Here we also find his relics (or at least his head). The interior of the chapel dates from the eighteenth century, when cardinal Pompeo Aldrovandi (1668-1752) ordered a renovation. The architects Alfonso Torreggiani (1682-1764) from Bologna and Domenico Gregorini (1692-1777) from Rome were involved in the project.
The most famous chapel in the San Petronio is the Cappella dei Re Magi, the fourth on the left. It is also sometimes referred to as the Cappella Bolognini, after a previous owner. The chapel was designed by Antonio di Vincenzo. Between 1408 and 1420 it was decorated with gorgeous frescoes by Giovanni da Modena. On the back wall he painted scenes from the life of Saint Petronius and on the right wall scenes about the three Magi. The most impressive fresco is, however, that on the left wall, where we see a Last Judgment with a Coronation of the Virgin and a representation of Hell. The central figure in the depiction of Hell is a gigantic and truly terrifying devil who devours sinners (see here for a good picture). Among the sinners is the Muslim prophet Muhammad (‘Machomet’), who can be found on the right above the devil. The image might make modern viewers feel somewhat uncomfortable, but in the fifteenth century there was nothing controversial about it. Jews were also portrayed in less than flattering ways on medieval frescoes (see here, here and here for examples).
The seventh chapel on the left is the Cappella di San Giacomo. Here we find a funerary monument for Elisa Bonaparte (1777-1820), Napoleon’s younger sister. In 1797 she married the Corsican Felice Pasquale Baciocchi (1762-1841). After her death she was buried in the San Petronio, and when her husband had passed as well, the beautiful monument bearing both their names was made. Above the sarcophagus with the names FELIX and ELISA we see the two spouses meeting each other at the gate of Heaven. The monument on the left side of the chapel was erected in honour of three sons of the couple who died young. The altarpiece in the chapel was painted in 1492 by Lorenzo Costa (1460-1535).
More work by Costa can be found in the Cappella di San Girolamo, the sixth chapel on the right side of the church. It should however be noted that the altarpiece in this chapel is only attributed to him. It can be dated to 1484 and depicts Saint Jerome. The second chapel on the right, the Cappella di Santa Brigida, also has several interesting paintings. The altarpiece is a polyptych featuring a Madonna and Child with Saints Paul, John the Baptist, Peter and James the Great. It was painted in 1477 by Tommaso Garelli (died ca. 1505). And then there are the most interesting wall frescoes of the chapel. On the left we for instance see a fresco of Saint Petronius from 1415, possibly by Giovanni da Modena, which also features the man who commissioned the work: he is sitting on the ground with his feet in the stocks. On the right wall we see a large fresco from 1417 that is attributed to Luca da Perugia. It depicts a Madonna and Child, with Saints Ambrosius, Anthony the Abbot, Petronius and Bartholomew to the left of them and Cosmas, Gotthard of Hildesheim (960-1038) and Damianus to the right. The sponsor of the work is also visible: this Bartholomew of Milan can be seen kneeling next to the throne. On the throne we can read the name of the painter.
As a final note I would like to mention the sundial in the church, made by the astronomer Giovanni Domenico Cassini (1625-1712) in 1655-1657. It replaced a previous sundial by Ignazio Danti (1536-1586) from the sixteenth century. Visitors may be familiar with the Linea Clementina, a sundial in the church of Santa Maria degli Angeli in Rome, but the sundial here in Bologna is almost half a century older and much longer.
 The story is told in John Julius Norwich, A History of Venice, p. 419. The casting of the statue and its fate are also discussed in Ross King, Michelangelo and the Pope’s Ceiling, chapters 4 and 25.