There’s something missing in our appreciation of the Renaissance, says Paolo Galluzzi, professor of the history of science at the University of Florence-something very important. While we rightly glorify this period as an extraordinary flowering of humanism and the arts, most of us have overlooked the engineering accomplishments that were just as much a part of the Renaissance as the “Mona Lisa.” Granted, we marvel at Leonardo da Vinci and his technological dreams of helicopters and scuba equipment, but our instinct is to consider him a preternatural, almost freakish figure plopped down in fifteenth century Italy-the definition of that aberration, “a genius.” In fact, Galluzzi explains, Leonardo represents the culmination of a century-long transformation of the technical arts and those who practiced them. To understand the Renaissance from an engineering perspective, he says, we must realize that Leonardo was no “lone visionary prophet in the desert.”

As curator of the exhibit “Mechanical Marvels: Invention in the Age of Leonardo,” which is on display at the Liberty Gallery in New York City until March 1, Galluzzi has provided us with the perfect opportunity to reassess the Renaissance. The exhibit focuses on the careers of four great artist-engineers of the Italian Renaissance: Filippo Brunelleschi, Mariano di Iacopo, Francesco di Giorgio, and Leonardo da Vinci. It features 50 working models of machines they devised as well as dozens of large-scale reproductions of their drawings and designs for these devices. The “mechanical marvels” include a three-speed hoist driven by oxen and capable of lifting loads of more than a ton to a height of 270 feet, a revolving crane, a mobile siege bridge, and a paddleboat, as well as such architectural masterpieces as the dome of the cathedral of Florence, 100 feet high and 165 feet across-a daring piece of engineering and construction that remains an enduring symbol of the Renaissance.

This remarkable exhibit depicts a transformation not only in the techniques available for modeling technology, but also in the profession of engineering. While the Middle Ages could claim impressive achievements and technological advances-from the great Gothic cathedrals to technologies like the heavy- wheeled plow and the horse harness and stirrup-the artisans who were responsible for these accomplishments remain anonymous and unsung. But by the height of the fifteenth century, Galluzzi explains, the artist-engineer had become “a socially prominent and respected figure, commissioned by powerful and wealthy patrons, well paid, and often regarded as one of the brightest ornaments in sovereign courts.”

What initially drove this transformation was rapid growth in commerce, intense urbanization, and-perhaps most important-a climate of great rivalry among the Italian city-states. The exigencies of competition, aggression, and security during this era were “a great engine for [technological] change, which is always the rather bitter irony of war,” notes Nicholas Adams, professor of the history of architecture at Vassar College and one of a number of experts who will lecture on various aspects of the Renaissance in conjunction with the exhibit. In this context, the engineer was greatly valued as a maker of military technology, says Adams. Even the young Leonardo promoted himself to potential employers by boasting of his abilities as a military engineer and designer of siege apparatus.

As the artist-engineer grew in social prominence, he sought to present himself as a learned member of the court, a philosopher, and perhaps most important, an author of texts. The Renaissance artist-engineers patterned themselves on such celebrated figures as Vitruvius, a Roman engineer and architect of the first century B. C. who codified the principles of architecture in a monumental work titled De architectura; they sprinkled their works with quotations (or more often, says Galluzzi, misquotations) from classical sources. But unlike Vitruvius and other classical scholars, whose treatises were long on text but short on illustration, the Renaissance engineers integrated text and images in a revolutionary manner. In doing so, they developed many far-reaching innovations in graphic representation.

The artists-engineers of the Renaissance discovered the laws of perspective and the techniques of cutaway, exploded, and rotating views. They pioneered the thinking sketch, the working drawing. As Eugene Ferguson wrote in Engineering and the Mind’s Eye, this “series of fundamental graphic inventions … greatly enhanced the precision with which a vision in one person’s mind might be conveyed by material means-drawings-across space and time to another person’s mind.” This crucial development both enabled and reflected the evolution of engineering from a workshop-based, case-by-case approach to a discipline rooted in principle and theory.

Prior to the Renaissance, design and construction were based almost solely on scale models fashioned by the hands of artisans. “Models are great,” Adams says, “because they show you in three dimensions how things are going to look and work.” Drawing, however, is quicker, cheaper, and more portable; it allows ideas to be transmitted across distances. “What’s interesting,” he adds, “is that the intellectual and conceptual effort that drawing involves becomes the engine for further development. It becomes a means of invention, of innovation.”

In the careers of the four artist-engineers featured in “Mechanical Marvels,” we can see how technical drawing evolved hand in hand with the changing role of the engineer. Filippo Brunelleschi (1377-1446) was the first Renaissance builder to break from the engineer’s traditional and largely anonymous role as a provider of technical services. Best known today as the man who designed and built the dome of Santa Maria del Fiore, he earned greater renown among his fellow engineers for the construction machines he invented to build it, such as the revolving crane shown on page 54. The ambitious scale and complex nature of the construction projects that Brunelleschi undertook certainly must have required him to draw, but none of his drawings survive. Like his contemporaries, he may have destroyed them in accordance with the code of secrecy typical of medieval guilds. Nonetheless, the Florentine is credited, according to Eugene Ferguson, with discovering the mathematical laws of perspective and producing the first demonstrations of these principles around 1425. The rules he devised were later codified and published, providing a foundation for other artist-engineers who followed him.

Brunelleschi saw himself as a craftsman, not an author. It is in the work of two engineers who followed, Mariano di Iacopo (1382-1458?), known as Taccola, and Francesco di Giorgio (1439-1501), that we see the first big steps in the development of the engineer as author and illustrator. These engineers, both of Siena, were deeply engaged in a variety of the city’s ambitious military, construction, and hydraulic projects. But they also set out to distinguish themselves as authors, compiling technical writings with innovative illustrations. “The artist-engineers of Siena grasped the tremendous interpretative and expository potential of graphics,” Galluzzi says, and they consciously devised ways to turn it into a powerful tool in their writings.

Taccola set out to recover the technical wisdom of antiquity. He discovered that often the best way to understand a difficult text was to make a visual translation of it. The techniques of the cutaway and exploded views (still indispensable for assembly, operating, and repair manuals) originated in his notebooks. He did not stop at explicating the ancients, however, but went on to fill several volumes with drawings of machines and inventions, ranging from military weapons such as trebuchets (see facing page) and hull-piercing devices to advanced fishing technology and waterwheels designed to capture the energy of the tides-a compendium that blends engineering dreams and a search for practical solutions, Galluzzi observes. And in a touch that expresses the continuity of the Sienese tradition, he notes, the final pages of one of Taccola’s manuscripts were completed in the hand of Francesco di Giorgio.

Francesco’s own writings make clear that he studied Taccola’s texts closely. The so-called Vatican codicetto, a tiny notebook filled with notes and drawings modeled on Taccola’s manuscripts, illustrates the learning process that characterized the Renaissance workshop: observation, imitation, and refinement of a predecessor’s work. The codicetto was obviously “a compendium for personal use,” Galluzzi observes, “a pocket notebook whose only unusual feature is the parchment sheets, which would normally have been quite extravagant for such a purpose.” Then again, Francesco probably used-and reused-these pages for a decade or more.

Like Taccola, Francesco undertook an ambitious project of illustrating a vast catalogue of machines, the Trattato di architettura. What was distinctive in Francesco’s approach, however, was that he tried to order these machines according to general rules. He categorized devices as either mills, pumps, pulling and lifting machines, or wagons, and provided commentary on materials, construction, specific applications, and even hints on ways to reduce wear and tear. Moreover, within a basic category, such as mills, Francesco would present as subcategories water mills, windmills, human- and animal-powered mills.

What was significant about this mechanical taxonomy, explains Galluzzi, was that it represented “the gradual emergence of criteria for describing machines by type and category based on the identification of common principles.” Based on his study of these devices, Francesco was able to design new machines far more advanced in mechanical design than Taccola’s.

It was Leonardo da Vinci (1452-1519), of course, who initiated the most ambitious expansion in the role of the artist-engineer, progressing from astute observer to inventor to theoretician. In his notebooks, which combined text and illustration, we see what are truly “thought experiments” in all kinds of areas, Galluzzi says. He analyzed, in almost anatomical detail, the “elements of machines” and combined them in innovative ways, such as in the complex spring motor. Drawing played a key role in this effort: it allowed Leonardo skillfully to dissect mechanical devices and reassemble them using the full range of illustration techniques he had mastered. His drawing of Brunelleschi’s revolving crane is one such example-in fact, the model currently on exhibit was built according to the specifications found in Leonardo’s sketches.

As his interests extended to other subjects-optics, hydrology, geology, and ultimately the human body-his studies were informed by his fascination with machines. For instance, Leonardo presents the human body, says Galluzzi, “as a remarkable ensemble of mechanical devices.” He sketches muscles, joints, and the motions of limbs in terms of wedges, axles, fulcrums, levers, and counterlevers-“the outcome,” Galluzzi notes, “of a bold attempt at unifying nature under a small number of universal laws.”

And again it is drawing that provides a new dimension to these investigations. In Leonardo’s view, drawing was indispensable if a machine or body or phenomenon was to be truly and wholly known. “O writer, with what letters will you describe with such perfection all that is depicted here in drawing?” asked Leonardo; “… don’t try to convey to the ears those things that pertain to the eyes, because the painter will be vastly better at it than you … . Therefore it is necessary to draw as well as to describe.”

What the Renaissance artist-engineers devised, Adams explains, was a way of working through the medium of drawing. “Leonardo comments on his copy of Francesco di Giorgio’s treatise,” he says, “and Francesco makes notes on his copy of Taccola. There is an internal commentary on drawing that is taking place, an internal discourse. There was nothing like this in earlier periods. What we have in the Renaissance are drawings about ideas, drawings about experiments.”

Leonardo was the grand master of this form of experimentation, Adams adds: “He just drew and drew and drew and created more and more ideas. And though relatively few of these ideas were actually realized, what’s important is that he kept developing the language. And it’s this language that becomes the basis for scientific experimentation and technological development in the centuries that follow.”

Today we take for granted the scientist’s and engineer’s notebook filled with questions, notes, quotes, drawings, scribbles, and erasures. But it was the Renaissance artist-engineers who invented the form. We see in their texts and drawings the complex interplay between practice and theory, and the overlapping aims of art, science, and technology. “Depicting nature, understanding nature, and modifying nature were all intertwined,” says George Bugliarello, former president of Polytechnic University, “and artists, engineers, and scientists alike were all engaged essentially as researchers.” In the work of the fifteenth century artist-engineer, he says, it is difficult to determine where the engineering begins and the science or art ends.

The Renaissance represented a rejection of constraints and an embrace of artistry that contemporary engineers would do well to emulate. As Eugene Ferguson observed in Engineering and the Mind’s Eye, “The conversion of an idea to an artifact is a complex and subtle process that will always be far closer to art than to science.” What “Invention in the Age of Leonardo” presents so strikingly is a reminder of how inspiring the blurring of those boundaries can be.