Arriving in Florence, the Chinese delegations would have seen towering above them the massive dome of the Cathedral of Santa Maria del Fiore, a symbol of religious faith and a tribute to Florence’s brilliant architects and engineers.

An argumentative, opinionated genius, Filippo Brunelleschi, was the cathedral’s architect. To build his creation, he had designed a lift to hoist up the four million bricks the job required. A novel invention, the lift could operate at two speeds, depending on the load, and was capable of reversing direction without stopping the bullocks that supplied its power. Once the bricks arrived at the base of the cupola, giant cranes, another ingenious design, shifted them into place.

The dome was unique, resembling a lemon with the bottom sliced off. Standing a sliced lemon upright, with the severed section as the base, one sees the curve increase as the dome rises. Initially, the cathedral bricks rise vertically, then they curve more and more as the tiers get higher, until, at the top, they are almost horizontal. Without internal supports to secure them, one would have expected the bricks to fall inward. But Brunelleschi solved this problem by deploying complex, three-dimensional mathematics applicable to the volume of inverted cones—an extraordinary solution he reached with the assistance of Paolo Toscanelli.1

Brunelleschi designed and organized everything concerned with this huge structure, at the time the largest in the world after Santa Sofia in Byzantium. He supervised the kilns where the bricks were made; he specified the proportions of lime and sodium bicarbonate for the mortar; he designed new forms for molding the bricks. He even built his own ships—articulated to facilitate sailing along the shallow, twisting Arno loaded with marble from Carrara quarries. He was granted a patent for this invention, accompanied by the right to burn rival boats! For three years, all marble was carried in Signor Brunelleschi’s barges. It appeared that Brunelleschi, like Leonardo da Vinci, never went to university yet he became a genius who could turn his hand to anything.

The city that sprawled around the cathedral in the 1430s was one vast building site, a frenzy of civic works.2 The dome alone created thousands of jobs; bricklayers, masons, carpenters, blacksmiths, winchers, plasterers, and tool sharpeners toiled like worker bees. Contractors quarried stone from the surrounding hills, providing marble from Carrara, Siena, Monsummano, and Campiglia. Florence’s lead furnaces fired full blast; tile and brick factories in Castinno, Lastra, Campi, and Impruneta worked in shifts at full capacity. Farmers planted new vines, sank new wells, and raised more barns.

Between the acquisition of the port of Pisa in 1406 and that of Livorno in 1421, Florence had enjoyed a continuous economic boom. Merchants made fortunes and patronized a stream of architects, sculptors, painters, and engineers. In this extraordinary era, Florence reached her apogee, “throwing up geniuses with the ease of a juggler.”3 Or so it seems.

Italy in the fourteenth century was a patchwork of small, independent states of negligible political and military weight. Dialect, money, even weights and measures varied from state to state. Florence itself was a backwater. Yet from 1413 to 1470, Florence produced a series of works so majestic that nearly six centuries later they can still take your breath away. Why did the Renaissance suddenly explode in this small Italian town? What caused Gothic architects, sculptors, and painters to adopt the radical style we call Renaissance? How did such a bounty of genius emerge from obscurity in the space of a few years? Why there? Why then?

One explanation begins with the fact that Nature was very kind to northern Italy. The Alps sweep in a defensive semicircle around her northern frontiers; in spring, their melting snows feed the Po and its tributaries, which meander across the plain of Lombardy to the Adriatic. Rain falls throughout the year; even in high summer the hay fields are lush and green, the sweet corn nine feet high. Three or four crops provide winter fodder for animals. Brilliant sunshine, abundant water, and rich alluvial soil produce crops of every description: walnuts and chestnuts in the mountains; apples, pears, grapes, and peaches in the foothills; on the Riviera, oranges, lemons, and persimmons. From Alexandria to Mantua stretch mile upon golden mile of rice fields. Four thousand square miles of intensively cultivated land in the Po Valley provide plentiful food for everyone.

Italy enjoyed other blessings, as well. Throughout the Middle Ages, life there differed from life in the barbarian north.4 The urban life created by the Romans survived the Ostrogoth and Hun invasions. After the fall of the Roman Empire, Italians (unlike the brutish English) were not driven back into forests. Feudalism did not take root (Italy provided few warriors for the Crusades).

Northern Italy had a far more dense population than elsewhere in Europe. Urban wealth and commerce had encouraged an inflow of labor from the countryside, stimulating further economic growth. Old Roman walled cities afforded protection. Cities, rather than states or kings, dominated northern Italy’s life. People were born, lived, fought, and died as individuals.

For millennia, Venice had been the hub of European trade, exchanging the riches of the East for raw materials from the north. Venice’s wealth spilled over into the Veneto and along the valley of the Po. Genoese, Florentine, and Venetian merchants set up business in Alexandria, Byzantium, and Trebizond. In northern Europe, by contrast, generations struggled to eke out a living in the cold forests and marshes surrounding them. There was little surplus labor for commerce.

Florence, nestled in the lee of the Apennines, enjoys a host of natural advantages. An easy journey from Venice, she is approached through lush, green valleys, their gentle, undulating slopes covered with oaks, sweet chestnuts, mountain ash, and acacia. Despite calamitous floods, on balance the River Arno has profited the city, providing an abundance of fish while transporting sewage and building materials downstream. Florence has never been much troubled by the water shortages that limited growth in the hill towns. Almost every aspect of the wool trade—separating fleeces, tanning hides, washing, spinning, and fulling—required copious amounts of water.

By the fourteenth century an all-weather road had been built beside the Arno. Traffic from Venice and the Lombard plain converged at Bologna, from which the shortest route to Rome lay across the Apennines. Florence occupied both trade routes—from the Adriatic to the Mediterranean and from Venice to Rome.

Florence’s access to Venice enabled her to reap some of the benefits of Venice’s trade with the East. It also exposed the city to an influx of Chinese and other Asians, as we can see from period paintings and sculpture. “About this time,” explained art historian Bernard Berenson in Essays in the Study of Sienese Painting, “the arts and crafts of the contemporary orient were beginning to invade Italy.”5

Ambrogio Lorenzetti, who never left Tuscany, painted The Martyrdom of the Franciscan Friars in the church of San Francesco Siena, depicting Chinese merchants with conical hats. Previously, oriental eyes had appeared in faces painted by Giotto and Duccio. As Leonardo Olschki wrote in “Asiatic Exoticism in Italian Art of the Early Renaissance,” “the impression has been given that Tuscany was almost a neighbouring country of the great Mongolian Empire and that Mandarins, Khans and Oriental dignitaries were almost as much at home in Florence and Siena as in Peking, Tabriz and Calicut.”6

There was a very substantial Chinese and Mongolian population in Florence in the decades after 1434, which Olschki describes here:

By this [slave] trade the Mongolian type became very familiar in Northern Italy and especially in Florence where the most conspicuous families such as the Adimari, Alberti, Cavalcanti, Medici, Strozzi, Vespucci and many others had their servants “de genere Tartarorum” and were emulated by notaries, priests, physicians, merchants and finally craftsmen and artists…. An ancestor of Alesso Baldovinetti bought three of those exotic girls whose portraits he drew on the margin of his still unpublished Journal…. The Mongolian slave girls seem to have been attractive enough to the Florentine male folk to become a disruptive element in the family life and general morality of the town. It is symptomatic that a lady of the rank of Alessandra Macinghi Strozzi wrote jocosely, in 1464, about a girl slave flirting with her son and behaving like a lady of his household. There is evidence enough for the important part played by these women in the amorous life of the town. Figures speak an impressive language. Among the 7534 infants delivered between 1394 and 1485 in the Florentine foundling hospital up to 32 percent were illegitimate children of those oriental slaves.

In this way a large influx of Asiatic blood penetrated into the Tuscan population during the most brilliant epoch of its cultural and economic evolution.7

Florentine families were able to keep Asian slave girls due to the wealth generated by the wool and silk trade. But that trade would never have flourished without the innovations of Italian banking.

Florence produced two bankers of genius: Giovanni de’ Medici and Francesco di Marco Datini.8 From 1398 until his death in 1410, Datini devised a range of new financial instruments that revolutionized European banking. Giovanni de’ Medici took over where Datini left off,9leading his family to become the wealthiest in Florence and far and away the most important patrons of Renaissance learning and art. The Medicis funded artists, astronomers, engineers, architects, and cartographers on a grand scale.

In addition to art, the family purchased power, assiduously courting the papacy. During the schism that resulted in two competing popes, one in Avignon and the other in Rome, a pirate rejoicing in the name of Baldassare Cossa was elected Pope John XXIII. The Medicis had bought Baldassare his cardinal’s hat with a loan of ten thousand ducats. When Baldassari became pope, the Medicis promptly became principal bankers to the papacy. (For a short period the Spinis replaced them, but at the end of 1420, the Spini bank became insolvent and the Medicis acquired their business.)

In 1421, for the statutory two-month period, Giovanni de’ Medici occupied the office of gonfalonieri, the head of Florence. Within a few years not only did the Medici bank became the most successful commercial enterprise in Italy but the family became the most profitable in the whole of Europe. For the next 150 years, Medici power and money fired the Renaissance.

The Renaissance produced an enormous appetite for talent—engineers, astronomers, mathematicians, and artists whose individual works were so widely acclaimed that others were inspired to follow with confidence. In this, Florence once again had an ideal climate.

While the Medicis and other wealthy patrons provided the funds, substantial projects were overseen by the operas,10 committees comprising of a cross section of society. Artists, engineers, and bankers sat alongside lawyers, astronomers, and aristocrats, just as they did in the city’s governing body, the Signoria. This relaxed communication among different social classes took place in a society that valued diversity. The Medicis counted the pope, the chancellor of Florence (Leonardo Bruni), Toscanelli, Brunelleschi, Leon Battista Alberti, and Nicholas of Cusa among their friends. They ate, drank, and prayed together, frequently meeting every day. They examined almost every aspect of human endeavor with a cold, inquisitive eye. If man could explain the fundamental workings of the heavens, he could expound with equal comfort on sculpture, painting, drama, poetry, music, medicine, civil engineering, and warfare.

A very important tradition, which bound the Florentine hierarchy together, was their private group meal, the mensa, held twice a day at the headquarters of the Signoria in the Palazzo Vecchio. As Timothy J. McGee wrote in “Dinner Music for the Florentine Signoria, 1350–1450”:11 “The Mensa took place in the civic office building now known as the Palazzo Vecchio which has served as the seat of Florentine government since its construction in 1300…. The Signoria was the executive branch of the city government…. Present at the mensa itself were a few senior members of the signoria staff (the famiglia), occasional distinguished visitors and guests of the city….”

The Chinese delegation, with their new ideas, fabulous inventions, and depth of culture, would have made a very forceful impression on Florentine intellectuals meeting for the mensa, including Paolo Toscanelli. Florence was the ideal loam for Chinese intellectual seeds.

By pure chance, the Chinese arrived in Florence just as the Medicis returned from exile. In September 1433 the Signoria had exiled Cosimo de’ Medici along with most of his family. However, in the elections of September 1434, the conservative faction in the Signoria was routed. The Strozzis, opponents of the Medicis, were exiled or barred from office.

Finance for the winning side had been provided by Cosimo, who had become chief executive of the family bank in 1420. He proved to be a brilliant banker. Profits for the years 1420–1435 totaled 186,382 florins and rose to 290,791 florins between 1435 and 1450. It was a huge sum, more than the income of some European states. Cosimo opened branches in Ancona, Pisa, Genoa, Lyons, Basel, Antwerp, Bruges, and London, becoming the first European international bank. He financed the Council of Florence (1438–1439) and provided the funds to topple the Viscontis in Milan, Florence’s old rival.

As Mary Hollingsworth has shown, Cosimo took a dramatic turn after 1434, embarking on an orgy of patronage. He financed exotic palaces and chapels—San Lorenzo, San Marco, and the Medici Palace—fitting them with magnificent libraries. He financed the production of new books, maps, and scientific instruments to fill them. Vespasiano da Bisticci, a leading Florentine bookseller, described Cosimo employing fifty-five scribes to copy two hundred texts—a small undertaking by the standards of Zhu Di’s encyclopedia but vast by European standards. (Henry V of England owned twenty books when he died in 1422.)

The Medici family spent 663,755 florins on patronage between 1434 and 1471. Recipients included Pope Eugenius IV, Toscanelli, Alberti, Poggio Bracciolini, Friar Mauro (for the world map of 1459), Christopher Columbus (described in chapter 10), and the young Amerigo Vespucci.12

The family supported Florentine humanists such as Toscanelli and Alberti, who showed a new approach to the world, explaining it through reason rather than mysticism. Cosimo financed artists who used perspective and proportion and scientists who argued that the earth was a globe, who could envision new lands full of riches that could be reached by sailing across the seas and never falling off the edge. He supported and financed scientists who could explain man’s place in the universe.

Mary Hollingsworth cites Cosimo and his brother Lorenzo’s embellishment of the sacristy at San Lorenzo as a notable insertion of science into the very heart of the church:

In the little dome above the altar, an astronomical fresco depicted the position of the sun, moon and stars for 6 July 1439, the official day of Union between the Eastern and Western Churches signed at the Council of Florence…. His choice of such an explicitly modern theme to commemorate this event was significant. Ceilings painted blue and studded with gold stars to represent Heaven were common in medieval churches. But this scientifically accurate depiction of a particular day’s sky was unfamiliar…. 13

The position of the sun, moon, and stars for July 6, 1439, as seen in Florence may be checked by setting up the software package “Starry Night” for that day at latitude 43°48' N. The puzzling question is, how did Cosimo’s artist—without the benefit of computer-based astronomical tables—know the position of the sun, moon, and stars for that day?

My first thought on seeing the painted heavens on the blue dome above the altar was that the artist must have had some sort of camera to photograph the sky so accurately. The mystery deepened after I studied color photographs of the dome, which displayed detailed celestial information.

Someone knew the precise positions of the stars relative to one another, as well as the positions of the sun and moon relative to each other and to the stars. Whoever painted that fresco understood the solar system. Author Patricia Fortini Brown, in “Laetentur Caeli: The Council of Florence and the Astronomical Fresco in the Old Sacristy,” states: “This is not just another star-patterned vault: with its carefully defined celestial meridians and graduated band of the ecliptic, distinctly marked off in measured degrees, it represents a dated and located sky with apparent ‘scientific’ exactitude.”


Canis Major as depicted in Alberti’s night sky in the Sacristy of San Lorenzo.

As described in chapter 4, the apparent position of the stars relative to sun and earth changes daily over a 1,461-day cycle. Because of the astonishing accuracy of the fresco, it is possible to date the day in this cycle that the fresco represents. Brown explains:

The recent development of computer based astronomical tables which accord a degree of accuracy unavailable to Warburg’s astronomer [a previous attempt at dating] now makes it possible to ascertain with certainty the date indicated by lunar and solar positions in the old Sacristy fresco…. Professor John Heilbron has been able to verify independently the 6 July 1439 dating first mentioned by Bing and to fix the time of day at approximately 12 noon.14

At noon on July 6, 1439, a mass celebrated the triumph of Pope Eugenius IV, who, at the Council of Florence the day before, had sealed the union of the western and eastern Christian churches. (With the union achieved, Venice’s navy subsequently defeated the Ottoman navy and lifted the blockade of Byzantium.) July 6 was named a public holiday, and the Cathedral of Santa Maria del Fiore was prepared with thrones for the Catholic and Orthodox bishops. Pope Eugenius IV celebrated a pontifical mass at noon with the epistle and gospel read in both Latin and Greek. The Decree of Union was then proclaimed in a papal bull, which began, “Laetentur caeli,” Let the heavens rejoice.

The dome was later painted to depict the moment of heavenly rejoicing. But how was it painted with such accuracy, and by whom?

My first thought was that the painting was done by observation of the sky. On examination, I realized this was impossible. It was broad daylight; although the stars were indeed in the positions revealed by the dome, they could not have been seen at noon.

What if the sky had been observed on the night of July 6, and the star positions extrapolated backward? This suggestion fails for two reasons. First, the fresco shows sun, moon, and stars, but the sun, of course, is not visible at night. Second, an army of observers would have been necessary to measure precisely the angles between stars and between the stars, sun, and moon—all at a time when the sun was not visible. Florence in 1439 had neither an army of qualified observers nor sufficient measuring instruments.

This complex painting required years to execute, during which the position of the stars relative to the earth would have changed according to the 1,461-day cycle. Thus it could not have resulted from piecemeal observations over the course of the job. Instead, the inescapable conclusion is that the artist had access to accurate astronomical tables.

From the financial accounts (quoted by James Beck, listing payments to the artists in Leon Battista Alberti and the Night Sky at Sun Lorenzo),15 it appears that the painting was started after the death of Giovanni and his wife, Piccarda Bueri, in April 1433, possibly halted during the Medicis’ exile (October 1433–October 1434) and started again in 1435, later payments being made in May 1439 and January and September 1440. The painting thus took at least six years. The explanation for the astonishingly accurate dating seems to me that the constellations with their figures (the major part of the work) were painted over six years up until the Union of the Churches, after which specific stars were painted in positions they would have occupied at noon on July 6, 1439—a relatively minor and easy piece of work if the declination and right ascensions of the stars were known.

Beck, has shown that the painter was Leon Battista Alberti, perhaps assisted by his friend Paolo Toscanelli. These two were Florence’s leading astronomers and mathematicians in 1439. Alberti in 1434 had accompanied Eugenius IV to Florence, where he met Toscanelli.

As we shall shortly discover, the most likely explanation of the fresco mystery is that Alberti, who served as the pope’s notary, met the Chinese delegates and obtained a copy of the astronomical calendar presented by the Chinese to Eugenius IV. The calendar provided the necessary information of right ascensions and declinations of stars to draw the night sky for a particular day and hour.

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