The Da Vinci Notebooks at sacred-texts.com
Imola as regards Bologna is five points from the West towards the North West at a distance of 20 miles.
Castel San Pietro lies exactly North West of Imola, at a distance of 7 miles.
Faenza, as regards Imola lies exactly half way between the East and South East at a distance of 10 miles; and Forli lies in the same direction from Imola at a distance of 20 miles; and Forlimpopolo lies in the same direction from Forli at a distance of 25 miles.
Bertinoro is seen from Imola two points from the East towards the South East at a distance of 27 miles.
243:571 : Leonardo inserted this passage on the margin of the circular plan, in water colour, of Imola--see Pl. CXI No. 1.--In the original the fields surrounding the town are light green; the moat, which surrounds the fortifications and the windings of the river Santerno, are light blue. The parts, which have come out blackish close to the river are yellow ochre in the original. The dark groups of houses inside the town are red. At the four points of the compass drawn in the middle of the town Leonardo has written (from right to left): Mezzodi (South) at the top; to the left Scirocho (South east), levante (East), Greco (North East), Septantrione (North), Maesstro (North West), ponente (West) Libecco (South West). The arch in which the plan is drawn is, in the original, 42 centimetres across.
At the beginning of October 1502 Cesare Borgia was shut up in Imola by a sudden revolt of the Condottieri, and it was some weeks before he could release himself from this state of siege (see Gregorovius, Geschichte der Stadt Rom im Mittelalter, Vol. VII, Book XIII, 5, 5).
Besides this incident Imola plays no important part in the history of the time. I therefore think myself fully justified in connecting this map, which is at Windsor, with the siege of 1502 and with Leonardo's engagements in the service of Cesare Borgia, because a comparison of these texts, Nos. 1050 and 1051, raise, I believe, the hypothesis to a certainty.