A historic centre of reference in Leonardo's projects for the Arno, in relation to the Padule, or marsh, of Bientina, known in the past as the "Lago di Sesto". We find Bientina on map RL 12685 (Windsor Castle), in the Codex Atlanticus and in Madrid Ms. II; the swamp or lake of the same name is also delineated by Leonardo, without naming it, on maps RL 12277 and 12279. In 1402 it was subjected to Florentine domination, except during the time of the incursion of Charles VIII into the territory of Pisa.
"Librafatta" is a reference point to the west in Leonardo's project for deviating the Arno. He represents the present-day Ripafratta, in the Commune of San Giuliano Terme, on map RL 12685, and mentions it in the Codex Atlanticus (f. 305r), in Madrid Ms. II (f. 52v) and in RL 12683. This stronghold was fundamental for controlling the valley of the Serchio and notably important also in relation to the Verruca.