How can we discuss the architecture of an architect who – so far as is known – built virtually nothing? The raw material comes largely from Leonardo’s sketches and notes, a rich profusion of original ideas and borrowings, and copies of drawings by contemporaries, such as Francesco di Giorgio Martini (1439-1502).

Martini was one of the most prolific military designers of his generation who, it should be said, also copied from Leonardo. This takes nothing away from either architect’s reputation. How else could ideas travel in the days before printing and printed illustrations transformed the spread of knowledge? For our purposes, Leonardo’s sketchbooks and their notes are the only guide to his architectural ambitions and provide the best clues to his elusive career.

Leonardo’s apprenticeship in Florence began in 1472 in the workshop of Andrea del Verrochio. In a later sketchbook Leonardo reminds himself to “keep in mind how the ball of Santa Maria del Fiore was soldered together.” This was a reference to the gilded globe which was made in Verrochio’s workshop before being fixed on top of the recently completed lantern over the dome of Florence’s cathedral some time between 1468 and 1472.

Leonardo may have witnessed this operation, and almost certainly was able to inspect the lifting equipment that would still have been in place when he arrived in Florence. Brunelleschi’s dome was the greatest architectural and engineering achievement of its age and Leonardo’s numerous sketches of its scaffolding, cranes, gearing systems, and blocks and tackle testify to his fascination.

Leonardo’s sketchbooks contain numerous examples of domed octagonal or circular churches, surrounded by symmetrical clusters of chapels covered by smaller domes or semi-domes. Explored both in bird’s-eye perspectives and in geometrical diagrams, the domed centrally-planned church was clearly an obsessive interest and this may well have had its origins in Brunelleschi’s scheme for Santa Maria del Fiore which served to “centralize” a Gothic cross-shaped church.

Later in life, Leonardo drew inspiration from Bramante’s circular Tempietto for the base of a proposed equestrian monument to the French general, Gian Giacomo Trivulzio. Throughout his career Leonardo seems to have been much more interested in the overall geometry of buildings than in the use of the orders and the classical detailing that was fast becoming the new orthodoxy in Italy.

In 1482 or 1483 Leonardo moved to the Milanese court of Lodovico il Moro, initially as a musician (according to Vasari’s Life). In Milan his activities expanded to include both civil and military engineering as well as three of his greatest artworks – the “Virgin of the Rocks”, the “Last Supper” (both begun in mid-1490s and finished much later) and the massive but never completed equestrian bronze statue of Duke Francesco Sforza (1401-66), which was commissioned by his son, Lodovico (1451-1508).

What might have been Leonardo’s greatest architectural project was also set in Milan. In the early 1480s the Milanese found themselves in a situation similar to that of the Florentines sixty years earlier, facing the need to complete an enormous unfinished Gothic cathedral by covering the crossing of the nave, transepts and choir. Brunelleschi had given the Florentines a dome, and unsurprisingly Leonardo’s competition scheme for Milan promised the same.

But this proposal found no support in a city still strongly influenced by Northern Gothic ideas. Before the Gothic tower and steeple was built between 1490 and 1500, a lively debate continued about the best way to solve the structural problems. The largest surviving group of Leonardo’s drawings on a single project are his sketches and diagrams of interlocking pointed arches for the vaulting system that would cover the crossing and carry the tower (which was much taller and heavier than the lantern over Brunelleschi’s dome). Having lost the dome, Leonardo was determined to be involved in one of the last great Gothic enterprises.

Town planning and surveying was another field of activity for Leonardo. His drawings for a city served by canals was probably prompted by calls for improvements following Milan’s disastrous plague of 1484-85, which killed some 50,000 people (one-third of the city’s population). Milan and its region was famed for canals, but Leonardo now proposed a two-level canal and street network with barges transporting heavy goods, and a separate upper street grid for “persons of quality” untroubled by heavy wagons, cleaned by the rainwater draining into the canals below, and serviced by public latrines and by spiral staircases connecting the two levels.

This was an age of ideal city designs as well as the launch of major urban developments such as Lodovico Sforza’s Piazza Grande in nearby Vigevano, and the Duke of Ferrara’s urban extension, the so-called “Addizione Ercole”, both started in 1492. Leonardo’s somewhat earlier city planning proposals for Milan are generally treated as a pragmatic response to dirt, disease and traffic congestion, rather than as blueprints for an ideal urban future; but his interest in canals, land drainage, water mills, pumping systems and hydraulics was to last his lifetime, culminating in proposals for a canal linking the Loire river system with a new town which he had planned for the King of France at Romorantin, near where Leonardo was to spend his last years. When the royal new town project was abandoned, Leonardo may well have contributed to the design of the central keep and double spiral staircase at the Chateau of Chambord.

Military machines and siege equipment are another continuous Leonardo theme, and a series of drawings (dated to the years 1497-1502) explore designs for fortifications with curved surfaces designed to deflect the impact of cannon balls fired by the gunpowder artillery that was then transforming warfare. The French invasion of Italy in 1494-95 set in motion a series of campaigns which removed Lodovico il Moro into French captivity and forced Leonardo to look for new employment in Florence. When he returned to Milan in 1508, it was occupied by the French. His most advanced fortification studies therefore coincided with real opportunities for military building in war-torn Italy.

Documented commissions from Cesare Borgia in the Romagna, the Appiani rulers of Piombino, and the Venetians at Gradisca all date from the turn of the century; but here too there is no firm evidence of completed works, and no opportunity to compare either new or modified works with the sketchbook designs. Leonardo’s fortifications – often circular in plan, and sometimes star-shaped in ways which can be seen to anticipate later developments – have been dismissed by some modern writers as fanciful and impractical. However they incorporate features encountered in the sketchbooks of men such as Francesco di Giorgio and the older Sangallo brothers who pioneered the new military architecture of Renaissance Italy. One of his schemes for low level pill-boxes around the base of a circular keep even re-appears in the drawings of Antonio da Sangallo the Younger who, in the 1530s, was planning a new fortress for Florence. Informed contemporaries clearly took Leonardo’s fortifications seriously. Perhaps we should do the same.

Content last updated: 20/04/2003

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