A drawing of a map covering about 2.5 miles (4 km) of the Arno, with north to the left. It depicts the river to the east of Florence, at the point where the railway now crosses the Arno. Damage to the embankment is prominent at the centre of the sheet where the river bends sharply, and further downstream where the water gushing through a weir strikes the bank. It is marked in units of 100 braccia (about 200 ft or 60 m), showing that it is drawn to a scale of about 1:10,000. Melzi's number 170. See also RCIN 912677, 912678, 912680.

Leonardo was a respected engineer and mapmaker. He worked as a military architect to Cesare Borgia, Marshal of the Papal Troops; he drew up plans to drain the malarial Pontine Marshes south of Rome; and he planned a great canal to bypass the river Arno from the sea to Florence. In the summer of 1504 Leonardo surveyed stretches of the Arno to the east and west of Florence, probably as a commission from the city government.

The Arno is a mountain torrent, low in the summer but prone to flooding in the spring and autumn, and the banks of the river required regular maintenance to keep its mills viable. Leonardo’s resulting maps are coloured with washes and complete with notes (written in the conventional direction) identifying mills, the sizes of sandbanks and so on.

Text adapted from Leonardo da Vinci: A life in drawing, London, 2018