This map dates from a period during which Leonardo was employed by the government of the Florentine republic on a variety of tasks, many of an engineering, cartographic or architectural nature. During the summer of 1504 he was apparently instructed to survey stretches of the river Arno east and west of Florence. From these surveys Leonardo constructed careful maps of both areas and then traced them in ‘fair copies’, RCIN 912678 and 912679, coloured with green and blue washes and with notes identifying mills, the sizes of sandbanks and so on.

The maps shown in RCIN 912677 - 912679 each cover about 2.5 miles (4 km) of the Arno, with north to the left; the scale bar on RCIN 912679 is marked in units of 100 braccia (about 200 ft or 60 m), showing that the maps are drawn to a scale of about 1:10,000. RCIN 912677 and 912678 cover the stretch from the Porta al Prato, the western gate of Florence, to the village of Peretola. 

The Arno is a mountain torrent, low in the summer (which allowed Leonardo to survey its bed during July and August) but prone to flooding during the autumn rains and spring thaw, and the banks of the river required continual maintenance. In the compilation of Leonardo's papers known as the Codex Arundel (London, British Library) are several pages of sketches and measurements done on the spot, together with records of living expenses incurred while on site.

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