Vitolini is never mentioned in the oldest written sources as a castle. Of its fortifications there is broad documentation beginning only from 1366, but the endowment of defensive structures must date back to the time when Vitolini definitively entered the orbit of Florence, which had long been pressing on the Valdarno border. In those years, as Villani narrates, the passage of militias encumbered the entire area of Greti and, in particular, Vinci, Cerreto, and Vettolino (Vitolini). The agreements stipulated between Florence and Pistoia in 1329 temporarily put an end to the most acute war phase, but from that moment on, Vitolini with Carmignano, Artimino, Bacchereto, and Castellina iusta Arni definitively entered the Florentine contado. For decades even Florence had to deal with the perennial state of war of this border line. It is in this context that, in all probability, Vitolini was equipped with a defensive apparatus suitable for the defense of the population of such an unstable territory. Of the material structure of the castle we have variant information, from one of the periodic visits made by the Ufficiali delle castella in the Florentine territory. In 1366, a long reconnaissance also involved the castle of Vitolini, which was the subject of a revision of the defensive apparatus. The walls followed the curving line pattern of the elevation and were equipped with battlements and wooden protruding apparatuses. They had two gateways, one on the east side and one on the west, mentioned in the 14th-century statutes, respectively, as Porta a Baccigno and Porta del Sole. From the western gate started the road to Vinci and Faltognano, while the eastern one led to San Giusto, from where one could go down on the other side of Montalbano. Some sections of the curtain wall had been occupied on the inside by houses built abutting with the wall, so that the officers had ordered they be equipped with walkways and brattices so as to ensure continuity of the defensive function of the wall against which they were supported. The statutes testify to the existence of a village underneath the embankments of the castle, also surrounded by walls. The church of San Pietro and a platea superior were most probably the market square, today's Piazza Mazzinghi, where until the last century there was a square-shaped tower. This new fortress of the defensive system of the Florentine border, as the 1366 report well explains, worked not only as a reference point for the inhabitants of the castle surroundings, but also for the communities of Santa Maria a Collegonzi, San Bartolomeo a Sovigliana, and San Donato in Greti. These three communities had to participate regularly in guard duty and contribute to expenses of the castle of Vitolini, which therefore functioned exactly as a castle-shelter for a large part of the population of Greti.