One of Leonardo’s most famous maps, folio RL 12278 of the Windsor Collection, includes a broad sector of central Tuscany. In one corner, we can see many of the tributaries on the left side of the middle valley of the Arno, including the Era, the Elsa, and the Pesa, with the stream Virginio. On this folio, Leonardo depicted a series of fortified villages that no longer exist. Leonardo was, in essence, the last witness to the landscape of castles and fortresses that formerly punctuated these hills, but which now have either partly disappeared or turned into something profoundly different. This route, accordingly, touches upon the "invisible" castles, like those of Tonda, or Camporbiano, some traces from which remain in modern tourist accommodation facilities, or like Mommialla, once a fortified house, whose ancient thermal waters have been brought back into activity. Remains of some of these fortresses can still be seen in the form of ruins in a wood, as for the case of the castle of Pietra, or along a road, as for Varna. In one case, it was only by means of archaeological excavations that the remains of the "invisible" castle were brought to light, as for Catignano. In other cases, there are majestic country villas standing today on the summits of the hills where the castles once stood, as for Granaiolo, Cambiano, and Montegufoni; in these, only the small churches remain from the "invisible" castles, now transformed into private chapels.