This general map of Tuscany and the Chiana Valley probably dates from the time when Leonardo was in the service of Cesare Borgia. It is presumably a strategic map produced for Borgia, for the place and river names have been recorded carefully. It may also have been produced in connection with Leonardo's plans to build a canal from Florence to the sea. Damming Lake Chiana was meant to guarantee a sufficient water supply for the canal, even during the dry season.
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