Among his memorable drawings exploring the relationship between man and nature, such as his anatomical illustrations and the studies of turbulent water flow, Leonardo da Vinci produced a number of mobile bridge designs. In a series of pen and ink drawings in the Codex Atlanticus, he experimented with solutions to this important engineering problem, one whose study exposes how he addressed problems of invention in the natural landscape through the practice of drawing.
In a single sheet from the Codex Atlanticus, fol. 55r, Leonardo illustrates two variations of a mobile wooden bridge in different stages of completion that include enlarged details and explanatory texts (fig.1). The drawing as a whole reads as a veduta, or view. A man perches on the end of the partially constructed bridge: his presence suggests its completion is a one-man job. With leg dangling, he attends a rope tethered to the next segment of pylon, now stretched taut where a branch in the water below has been secured. The man is one span shy of reaching the other side of the river. An element of bravura pervades the scene. The man is perched on a beam with only one supporting pylon staked in the water, but he signals his confidence not only in the structural design but also in the construction of the bridge itself.
As a safety buffer Leonardo introduces a clever clamping tool. A ring loops through the horizontal beam, attached to a toothed peg fit with a cog that can click up and down by means of a lever. That peg in turn has a ring that can be fit over the top of the vertical beam, thereby securing the two beams together. The clamp can then be simply adjusted farther down the line—the device appears twice more at the base of the second bridge below. Therefore this illustration renders the process of building as much as it depicts the design for the bridge itself. One can mentally extend the design and understand how the segments are attached to one another and how the whole is fastened to the adjacent bank. Leonardo also repeats and magnifies this anchoring detail in the right margin of the folio (fig. 2).
The text echoes this step-by-step instruction. In four marginal notes Leonardo explains that the intrinsic feature of the design is its speed of construction. Its ease of facture and the availability of materials result in a bridge molto comodo e presto—convenient and quick. At the top of the folio, Leonardo writes of the design rationale for the bridge and of its method of construction: "In this way one can quickly build a bridge so as to escape or follow the enemy." For either fleeing or pursuing, this design provided swift passage over terrain otherwise less readily navigable.
Mobile bridges work on a variety of territory and these drawings by necessity ground the devices in a particular terrain. They presuppose a relationship between technical design and illustration that aligns the generic design with site-specific characteristics. The drawings are as much about site-conditions and specificity, as they are about articulating a particularly useful mobile bridge design: note the knobbiness of the wood branches, the irregularity of the riverbank, the imperfect symmetry of the design. Leonardo presents just enough repetition of segments and knots and tools to render the design familiar and reproducible. His drawing persuades the viewer of the utility and adaptability of his bridges, hence the pains taken to underscore the jagged embankment.
Among his technical drawings, Leonardo's mobile bridges necessitate a particular kind of environmental fixity. They are architecture anchored to the land as much as they are clever tools, easily assembled and disassembled. The status of the mobile bridge as both architecture and mechanical device informs Leonardo's illustrations: the bridges are particularized and located in situ, yet designed to be infinitely reproducible and adaptable.
Various details indicate the material construction of the bridge. Leonardo includes hooked pieces of wood, casually laid out on the embankment (fig. 3): they are lashed in the middle, with the ends hooked like crochet needles to aid the binding together of the supports, in his words "come treccia," which means plaited or braided. Another sheet in the Codex Atlanticus, fol. 58-a verso, depicts at least three variations for knotting together wooden supports, rendered in front and back perspectives (fig. 4). His repositioning of the lashed beams corroborate his interest not only in how one might securely tie wooden supports but also persuasively and usefully demonstrate various knot techniques. These small sketches illustrate finished knots, ones that a sharp eye could mentally untangle. Likewise the bridge designs invite—even require—a kind of skillful rebuilding: one notices how to assemble the bridge, mentally completing the span in a cognitive process of visual reading. The viewer must discern the parts to assemble the whole, and the incompleteness of the design provides the insight in how to build.
Throughout his life, Leonardo studied the relationship between man and nature, particularly through the study of the science and management of water. Water's essentiality to early modern life cannot be overstated, and figuring out ways to harness, channel, or traverse it engaged the minds of artist-engineers and the financial resources of patrons. Leonardo participated in these efforts by devising large-scale hydraulic schemes, such as his ambitious plans to reroute the Arno River.
Among these undertakings, mobile bridges expose how the practice of technical invention was intertwined with an understanding of the variability and instability of the natural landscape. Leonardo employed drawing as a way to navigate nature. In their coupling of scientific and artistic practices, his drawings ultimately lead to pressing inquiries into the nature of knowledge and the knowledge of nature.
Fig. 1 Leonardo da Vinci, Codex Atlanticus, fol. 55r, c. 1483-87, Veneranda Biblioteca Ambrosiana, Milan.
Fig. 2 Leonardo da Vinci, Codex Atlanticus, fol. 58a-v, Veneranda Biblioteca Ambrosiana, Milan.
Fig. 3 Detail of Leonardo da Vinci, Codex Atlanticus, fol. 58a-v, Veneranda Biblioteca Ambrosiana, Milan.