The Architect & the Egg

Inspired by natural form, Brunelleschi’s famous Florentine dome remains the biggest of its kind ever built…

A church, of some sort, had stood at the site of Florence Cathedral since the fourth-century. Not surprisingly, by the thirteenth-century, it was no longer in a good state of repair and in dire need of an overhaul. The building of the ‘new’ cathedral began in 1296 and was not completed until 1436. That’s 140 years under construction.

The original designs for ‘Cattedrale di Santa Maria del Fiore’ were laid-out by the the architect and sculptor, Arnolfo di Cambio, and were startlingly different from the medieval fashion of the time. Seeking inspiration from classical buildings, he’d avoided towers, high arches, and flying buttresses. Thus, the building of Florence Cathedral signalled the decline of the Gothic and ushered in the Renaissance.

Hoping to recreate the grandeur of Rome’s Pantheon, he’d left room for a massive dome with a span of around 150 feet, but the secrets of such monumental scale construction had been long lost, as had the formula for the Roman structural concrete used in the dome of the Pantheon. When Arnolfo di Cambio died in 1302, he’d neglected to share any plans for that part…

Work on the Cathedral slowed and the local parishioners continued to use the smaller medieval church, still standing within the larger, incomplete structure being built around it. Construction resumed in earnest some thirty year later when Giotto di Bondone was placed in charge of the project. He managed to avoid working on the dome, instead concentrating on adding his impressive and aesthetically pleasing campanile tower.

After Giotto’s death in 1337, his collaborator Andrea Pisano stepped-up to oversee the continued construction for the next decade, until he succumbed to the Black Death in 1348. Thereafter, work on the cathedral was sporadic, directed by a series of architects who didn’t deviate significantly from the original vision of Arnolfo di Cambio. The ancient basilica within was finally demolished and the Cathedral’s nave was then completed by 1380.

There was just the one problem… A huge hole remained in the roof that needed to be covered with a vast dome! Not one in the succession of chief architects had managed to come up with a suitable solution and the cathedral remained open to the elements.

Among several artists to advise on the design and décor was Andrea di Bonaiuto da Firenze who was also working on frescoes for the Chapter House of the Basilica di Santa Maria Novella — another prominent Florentine church. One of his panels there, Allegory of the Militant and Triumphant Church, was intended to glorify the achievements of the Church in general and the Dominican order in particular.

Problem was, that Andrea di Bonaiuto had imagined the Cathedral topped with its impressively voluminous dome. The patrons liked his ‘concept art’ and anything less would now imply the church was not quite as triumphant as the fresco proclaimed… Of course, painting an imagined dome wasn’t the same as building a real one!

The patrons really needed to find an exceptional architect, capable of overseeing the construction of an ostentatious dome like no other. They attached an attractive fee of 200 florins to the commission yet no architect they asked thought it was possible to build such a dome.

So, they cast around outside the field and were intrigued when Filippo Brunelleschi, a local goldsmith with no prior building commissions, claimed he was the man they were looking for.

How did Brunelleschi convince the patrons to take a gamble on him when many of his contemporaries were also competing for such a prestigious job? Reputedly, it was all down to something he did with an egg…

The story goes that when he gave his pitch for the project, he had no plans to show! Instead, he presented the panel with an egg and set them a seemingly impossible challenge: He asked them to balance the egg on end.

After each of the patrons and masons had passed the egg round and failed his challenge, Brunelleschi took back the egg and with a decisive gesture brought it down onto the table top with just enough force to impact the shell at the blunt end, effectively flattening the small air space within the shell so that the egg stood stable and upright. No mess.

The panel dismissed his little trick, claiming that any one of them could’ve done that! Brunelleschi pointed out that, nevertheless, not one of them had. He knew that they were reluctant to entrust such grand work to a ‘newbie’ with no formal training but argued that if he explained his plans to build the great dome, then any architect could do that, too. They were impressed enough with this upstart’s audacity that they decided to take a chance.

It seems things did not go quite as smoothly as this oft-told tale suggests as there are also accounts of Brunelleschi, “a buffoon and a babbler,” being forcibly ejected from the assemblies on more than one occasion! Although they did finally award him the commission, his main competitor, Lorenzo Ghiberti, was appointed as his ‘supervisor’ on equal pay.

Also, once the contracts were drawn up, Brunelleschi did explain, in detail, the ingenious and highly original construction techniques he was to employ. He did this using scale models made out of precisely carved wooden blocks and would also carve explanatory maquettes out of wax and, on occasions, vegetables…

He had sought the solution not in the work of predecessors but in the study of nature — something that marks him as ‘a Renaissance man’. If grasped in a fist, it takes huge effort to crack a humble hen’s egg and the mechanical strength of such a fragile material had impressed him. He’d discovered how parabolic curves distribute force tangentially, giving such forms incredible load-bearing properties.

The religious significance of eggs would’ve also been an influence on his thinking. The oval had long been an alchemical symbol for the fifth element of spirit and the egg had become a Christian metaphor of the everlasting Holy Spirit. This association may date back 60,000 years to decorated ostrich eggs in prehistoric African culture. Eggs, often made from precious metals, were placed in the tombs of kings in ancient Egypt as a symbol of rebirth into the afterlife. Hence the traditional exchange of Easter eggs as gifts to commemorate the Resurrection. Originally, they represented Christ’s tomb and the potential of new life, sealed within.

Brunelleschi devised a way to build without the use of internal scaffolding, for which there wasn’t enough available timber anyway, thus enabling use of the church to continue uninterrupted. He employed an array of processes combined in unprecedented ways to build the dome that has survived to this day.

It is, in fact, two domes, one inside the other. The lower sections are built of stone, laid out in a series of smaller, overlapping curves. Each layer is stabilised by the weight of the one above and so forth. He solved the problem of lifting the masonry without using a traditional scaffold by ‘scaling-up’ his goldsmith’s experience of working with clock mechanisms. He invented a new, ox-driven pulley system that used an ingenious clutch and gear system with giant ropes that had to be specially made by shipwrights.

The inner ‘shell’ was strengthened by hoops of wood and metal that act like the restraining bands around a barrel. This prevented the load-bearing parabolic curves from distorting and was a new way of countering the spreading tendency without the use of hefty buttresses. The outer dome is stabilised with concealed chains attached to the inner.

The inner dome was built to be seen from the cathedral’s interior below, its concave surface suitable for decoration, whilst the outer dome was intended to be viewed from outside. Its convex surface was finished with brick, partially for aesthetic reasons, and because it was a much lighter material than stone.

The dome was completed by March 1436 though the finishing touch of the ‘lantern’ at its top was not added until 1461, posthumously created according to Brunelleschi’s design by his associate, Michelozzo di Bartolomeo Michelozzi.

The frescoes for the interior would be designed a century later by Giorgio Vasari who began the decoration in 1568. They were completed in 1579 by Federico Zuccari. However, the cathedral’s outer façade was not entirely finished until the nineteenth-century.

Brunelleschi had carried his egg theme right through from initial inspiration to final product. Not only has the shape provided an enduring structural integrity, it also works to visually compensate for foreshortening. When viewed from the streets below, the subtly elongated oval appears domed, rather than looking ‘flattened’ as a true hemisphere would. The completed structure was, and still is, the biggest masonry dome ever built.