From the Ruins of Rome to the Invention of Perspective

For the most part, humanism was a literary and philosophical movement focused on books and texts. Itinerant scholars such as Poggio Bracciolini traveled far and wide in an effort to locate lost ancient works that might be hidden away in the monastic libraries of Europe. Seeking out the most authentic versions, they worked hard to restore the texts to their pristine glory in their original tongues, mostly Greek and classical Latin, but also Hebrew, Arabic, and other languages. These newly recovered texts would then circulate among the humanists, replacing existing (and allegedly corrupt) medieval versions if such existed, or adding new ancient sources if they did not.

Filippo Brunelleschi (1377-1446), who would one day make his name as the designer and builder of the great dome of the Florence Cathedral, however, was not a literary scholar. A brilliant artist, architect, and engineer, he was not a man to spend his days poring over ancient manuscripts. For his humanist friends the passion for the ancients meant recovering the writings of Plato, Cicero, and Lucretius and returning them to their original brilliance. For the practical-minded Brunelleschi it meant something else: studying the physical traces of the ancients—the buildings, aqueducts, roads, and sculptures that they left behind. The humanists traveled to far-flung corners of Europe in pursuit of their original texts. Brunelleschi, in contrast, headed straight to the capital of the ancient world and the home of its greatest monuments: Rome.

At the turn of the 15th century, Rome had sunk to one of the lowest points in its long and illustrious history. Back in the 1st century C.E., as the capital of a great empire, the city had boasted a population approaching two million, making it by far the largest city in the Mediterranean world, and probably anywhere. But four centuries later, with the empire in steep decline, the population had dwindled to less than half that number. The barbarian invasions that followed, accompanied by the collapse of commerce throughout Western Europe in the early Middle Ages, saw the city’s population crash to a tiny fraction of its ancient heights. Even the revival of urban life in the 11th and 12th centuries, which saw ancient towns come to life and new ones spring up throughout Italy, did little to improve the fortunes of Rome.

While cities such as Florence and Venice grew into bustling centers of commerce and manufacture, the ancient imperial capital fell further and further behind. In time the popes of the Renaissance would rebuild and repopulate the city and make it a worthy capital of their spiritual empire. But in 1403, when Brunelleschi arrived, Rome was a poor and disease-ridden town of perhaps 30,000 souls, many of whom lived like vagabonds among the monumental ruins.

The young Florentine, however, had no interest in the sad, dilapidated Rome of his day. All he saw was the city’s past greatness: the remains of the great temples in the Forum; the seemingly indestructible roads, many still in use; the ruins of the massive aqueducts that had supplied water to the city of millions. Among the great structures still standing he surely would have noted the circular Colosseum, built by the emperors Vespasian and Titus in the 1st century C.E., and the monumental public baths built by the emperor Diocletian around 300 C.E., renowned for their high, vaulted ceilings. Most striking of all was the Pantheon, with its massive dome, whose span and height of 142 feet was still the largest in the world.

Brunelleschi, to be sure, did not come simply to admire the faded glory of the Eternal City: he was there to learn everything he could about the structures of ancient Rome, from simple abodes to great monuments, and to determine how they were built. As his biographer Vasari told it more than a century later, “his studies were so intense that his mind was capable of imagining how Rome once appeared even before the city fell into ruins.” If the humanists’ dream was to recover the intellectual world of Cicero, Seneca, and Tacitus, Brunelleschi’s was to recover their physical world—the streets they walked, the houses they inhabited, the temples in which they worshipped.

Rather than work alone, as was his habit, Brunelleschi this time was accompanied by a friend, the sculptor Donatello. Together the two Florentines set to work surveying every structure they could find: they “made rough drawings of almost all the buildings in Rome . . . with measurements of the widths and heights as far as they were able to ascertain,” Manetti tells us. Since the structures were in ruins, and the original street level was buried deep in the ground, this was easier said than done. It often proved necessary to dig up the structures’ foundations in order to determine their original shape and true height. When the job was too great for the two of them, they hired laborers, and when measuring heights and distances directly was impractical, they relied on geometrical measurement techniques, using surveying rods and mirrors. To record the measurements “they drew the elevations on strips of parchment graphs with numbers and symbols that Filippo alone understood.” And so they surveyed house after house, and ruin after ruin, over the entire ancient city.

Day and night the two Florentines labored on their colossal undertaking, but no one in the city understood what they were up to with all this digging and measuring. Lacking a better explanation, the Romans assumed the two were looking for gold or marketable goods, and so they became known in the city as “the treasure hunters.” The Romans may not have been the only ones confused, since according to Manetti even Donatello was partly in the dark about Brunelleschi’s true purpose. Secretiveness was to Brunelleschi second nature, and, as far as was possible, he kept his ideas from even his closest companion.

What, then, was Brunelleschi hoping to accomplish with his exhaustive survey of Roman antiquities? One goal, undoubtedly, was a professional one: Brunelleschi wanted to learn the construction methods of the ancient Romans so that he could make use of them in his own projects. For example, according to Manetti, “he considered the methods of centering the vaults and other systems of support, how they could be dispensed with and what method had to be used, and when.” Perhaps he was already devising the machines that he would use, years later, to build the great dome of Florence’s cathedral.

But there was something more to Brunelleschi’s “treasure hunt” than the acquisition of technical knowledge. Brunelleschi believed that the ancient architects designed their structures in accordance with perfect mathematical harmonies, which were responsible not only for the soundness of the buildings, but also for their beauty. His goal, according to Manetti, was “to rediscover the fine and highly skilled method of building and the harmonious proportions of the ancients.” Some of these harmonies were fairly straightforward: the interior of the dome of the Pantheon was an almost perfect half-sphere, and the classic columns used in all public buildings were constructed according to strict mathematical proportions. Ionic columns were nine times as high as the diameter of their base, Corinthian columns ten times their base, and so on.

Other symmetries and harmonies, however, could not be so easily discerned. Brunelleschi believed that the buildings of Rome harbored many more secrets, which could be uncovered only through painstaking systematic work. By surveying, measuring, and recording the heights, lengths, shapes, and distances of every ancient structure in Rome, he was hoping to uncover those hidden mathematical harmonies that guided the ancient builders of the Eternal City and had since been lost. In the hills of Rome others might see a haphazard and disorderly jumble of ruins in various stages of disrepair. Brunelleschi saw the outlines of a perfect, harmonious order that pervaded every structure—and the entire city.

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Even while still spending most of his days as a Roman “treasure hunter,” Brunelleschi made regular visits to his native city, where he remained  a familiar figure. And it was one of those visits, in or around 1413, on one morning when we find him walking briskly past the baptistery, site of painful memories, and toward the doors of the Duomo. He may well have been contemplating the great cathedral’s missing cupola, while nurturing a secret ambition that he would be the man to build it.

Yet the objects he was carrying that morning were not the tools of a goldsmith and caster of bronze, as one would expect of the master craftsman who had lost the competition for the baptistery’s doors by the slimmest of margins. Nor were they architectural designs or engineering plans, as later generations, who know him as the builder of “Il Cupolone,” might expect. A mirror and a painting with burnished silver and a hole in the middle are all that Brunelleschi held in his hand. In what must have been no more than a few hours, and using these simple objects, he forever transformed the way people perceive and experience the space around them.

Here’s what Brunelleschi did: First, he held the back of the painting to his face, placing the hole in its center before his eye. Manetti, who held the painting in his hands decades later, reported that the hole was “as tiny as a lentil bean on the painted side” and that it “widened conically” on the back side, reaching “the circumference of a ducat.” Brunelleschi pressed his eye to the cone and looked through the hole toward the baptistery. With his other hand he held up the mirror in front of the painting so that, instead of the actual octagonal structure, he saw its image in the painting reflected back at him. There was the baptistery and the buildings around it as he had painted them. There was the blue-gray sky, the drifting clouds, and passing birds captured in the burnished silver on the painting and now reflected from the mirror and back at Brunelleschi’s eye. From the peephole at the center of the painting, Brunelleschi was looking straight at the painting’s reflection in the mirror. The artificial image was almost indistinguishable from the view of the actual baptistery as seen from the same spot.

It was surely one of the most baffling scenes ever to take place before the ancient walls of the baptistery. From a distance it would have appeared that Brunelleschi was inexplicably covering his own face with the back of a painting; from close by, when the hole in the painting was revealed, it seemed that he was going to enormous lengths to see what was freely available to the naked eye—the octagonal outlines of the baptistery in the morning light. Why the painting, the peephole, the mirror, if the only purpose was to reproduce the exact scene that could be viewed without them? What, one might understandably wonder, was Brunelleschi up to?

The answer lies precisely in the bewildering identity of the natural view from the cathedral’s doorway and the artificial view of the painting and mirror that Brunelleschi worked hard to achieve. The whole purpose of the experiment, in fact, was to demonstrate that he had mastered the secret of the true representation of nature, one that differs not at all from the real thing. The more similar the mirror image of the baptistery—seen through the hole in the painting—is to the actual view from the Duomo’s doorway, the better. The best indication of the experiment’s success was if the mirror was suddenly yanked away, the view through the hole in the painting remained practically unchanged. Brunelleschi had succeeded in capturing a three-dimensional view of an object and then reproducing it from scratch on a flat canvas. Nothing like it had been accomplished before, but his contemporaries soon had a name for it: they called it perspective.

That Brunelleschi was widely considered the founder of perspective we know from his contemporaries: not only his biographers, Manetti and Vasari, but also the humanist Domenico da Prato, who wrote admiringly about “the perspective expert, ingenious man, Filippo di Ser Brunellesco, remarkable for skill and fame.” And Manetti’s friend Cristoforo Landino reports that “the architect Brunelleschi was also very good at painting and sculpture; in particular, he understood perspective well, and some say he was either the inventor or rediscoverer of it.” Sadly, however, Brunelleschi’s painting of the baptistery is lost to us. Manetti, writing decades later, tells us that he had held it in his hands and “seen it many times,” and it was listed among the effects of Lorenzo the Magnificent, Medici ruler of Florence, after his death in 1492. But that is the last we hear of it, and as a result we cannot know with certainty what exactly Brunelleschi did in the painting to earn him his reputation as the founder of perspective. Yet his use of a mirror in his experiment provides an important clue.

Introduced to Europe in the 13th century, mirrors were still rare and expensive items in Quattrocento Italy, the objects of widespread fascination. A mirror, after all, is a flat, two-dimensional surface, just like a wall or a painting. And yet when we look at a mirror it is almost impossible to maintain our awareness that the mirror is flat, because the perception of depth practically overwhelms us. We see our own reflection not on the surface of the mirror but behind it, just as we see all the objects around us deep in the mirror’s illusory space. Furthermore, all objects appear at the same distance “behind” the mirror as they are before the mirror’s surface.

Today we take mirrors and their images so much for granted that we hardly think them worthy of comment. Yet there is magic here: without any human intervention, mirrors produce a perfect three-dimensional image on a flat surface, one that is practically indistinguishable from the original. How do they do it? And what does an artist, using all the skill and human artifice at his disposal, need to do to reproduce the effect? This seems to have been the question on Brunelleschi’s mind as he was designing his experiment. If he could reproduce a mirror-like sense of depth in his painting of the baptistery, then the image the flat painting reflected back at the observer would appear not flat at all but three- dimensional. For an observer, it would be as if they were looking directly at the baptistery.

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Excerpted from PROOF!: How the World Became Geometrical by Amir Alexander. Published by Scientific American/FSG, a division of Farrar, Straus and Giroux, on September 10, 2019. Copyright © 2019 by Amir Alexander. All rights reserved.