Through his study of the landscape, Leonardo came to believe that vast changes had occurred in the distribution of water over the surface of the earth over aeons of time. This erosive power had shaped the forms of the landscape.

The landscape of the Mona Lisa is a testament to the awesome powers of nature that give form to all things. The jagged mountains have been eroded and fashioned by the flow of water over countless centuries. Within the rocky landscape, a track seen on the left appears also on the right. It seems to be a dried-up river-bed. Its connection to the lake seen higher up is unclear, but it may be a reference to a lake in primordial times that was believed to have formed when a huge rock barrier once damned the Arno.

Leonardo noted how this formed two huge lakes, “the first of which is where we now see the city of Florence together with Prato and Pistoia”. In the upper part of the Val d’Arno as far as Arezzo, a second lake was formed which emptied its waters into the first lake.

In Leonardo's words
The water which from the lowest depths of the sea entering by the force of its mover is driven to the high summits of the mountains, where, finding several veins, it hurls itself downward and returns by the shortest way to the depths of the sea; and again it rises through the ramification of the veins and then falls again, and thus up and down, turns inwards and outwards, after the fashion of the vine, the water of which pours through the severed branches and falls back to the roots, and again rises through channels and repeats the same descent.