During the summer of 1504, Leonardo was apparently employed by the Florentine government to survey stretches of the river Arno. This map shows a 400m stretch of the river, and the damage to the embankment caused by the waters passing through a weir. Two sections of damage are recorded, the first from the immediate impact of the current, and the second - as Leonardo demonstrates in the drawing - from the reaction of the energy of the current, curving back from the riverbank further downstream. The blue wash, the careful finish, and the notes on the damage in conventional left-to-right script indicate that the drawing was for someone else to see, presumably a government official.