The first document that provides information about the material constitution of the castle of Monterappoli is the 1254 deed of sale by which the Counts Guidi ceded to Florence castellaris Monterappoli sicut girant ripe et fovee. Judging from the text, which uses the term castellare, generally used to refer to a fortification no longer in use, the defenses of Monterappoli must not have appeared in good condition in the middle of the 13th century. The same text also shows, however, that the castle was once equipped with a defense system composed of, in addition to walls, banks and a moat before the wall, structures that still defined—probably along with what remained of the wall—the perimeter of the fortified center. The 1254 deed of sale of the castle also shows the first mention of the castle church dedicated to San Lorenzo, which is now visible, albeit in late forms, in the hamlet of Monterappoli (municipality of Empoli). At the beginning of the 14th century, however, the castle must already have recovered its defensive function. In fact, it turns out that it was the object of special attention by the subjects that gravitated around the border line of the Elsa, especially the city of Florence. In 1313 the inhabitants of Monterappoli obtained exemption from a tax obligation, owing to the high expenses they had incurred for the development of the defenses of their own castle. Documentation from the 14th-15th centuries produced by the dominant city enlightens us on the material constitution of the castle of Monterappoli in the Late Middle Ages. In 1368 the Ufficiali delle Castella ordered the expansion of the castle, then considered too small to accommodate the population that lived in the villas of the surrounding area. The 1393 statutes of Monterappoli confirm the fact that the restoration works for the castle defenses were still underway at that time. It was prescribed that the duties owed by foreigners were to be destined entirely for expenses for the castle walls, towers, and brattices (bretèches: small balconies with machicolations). The same defense works were the subject of special regulations aimed at their preservation. From the statutes we learn that many of the houses were built near the wall. Those who owned houses next to the castle wall were responsible for the maintenance of the wall itself and for the efficiency of the defense. Specifically, the construction of a masonry channel was ordered, to drain rainwater to the exterior of the castle wall in order to avoid its rapid deterioration due to rains. Inside the castle, in addition to the church, there was also a building known as the "house of the municipality" (town hall), equipped with loggia, located in a public space inside the castle and intended for housing the municipality's officials. A century later, the castle seems still to have been equipped with defensive structures, but decidedly more articulated. From the 1427 land registry declarations, the inhabited area appeared to have divided into an older nucleus, the Chastelvecchio, and a more recent part, the Castelnuovo. The former included most of the residents' homes, in many cases adhering to the castle walls, some in good condition, others apparently crumbling (claiming, for example, "the house is propped up by supports"). The inhabited area had its own internal road system: mentioned, in fact, was a significant Via delle Liti. In Castelvecchio stood also one of the most complex buildings of the entire town (a worker's house and a house for the lord, with a cell and other buildings, with harvesting barrels) that bordered the town hall. If we can hypothesize, for these building complexes, a construction technique made of stone, we do know that in other cases, the castle houses might be constructed of raw earth (casa di terra). The other sector of the inhabited area, the so-called Castelnuovo, would appear to coincide with an area of civic expansion called borgo di San Piero. Documentation indicates that there were some dwellings that bordered with the "old ditch" (the castle moat). There was also the casa dello spedaliere, the house of the rector of a reception structure located outside the town, in the locality of Romitorio. This is roughly the aspect under which Leonardo depicted Monterappoli on his map RLW12278. The Valdelsan village is represented as a castle still equipped with a defensive circuit, equipped with towers. At the beginning of the 16th century, therefore, the castle of Monterappoli still had the material constitution and appearance that it had assumed during the Late Middle Ages, although the first signs of transformation of the defensive system were already underway. In 1507, in fact, a request had been made for the purchase of part of the moat and the banks, evidently no longer in use. Again, in 1511, a Florentine citizen, a certain Pier Maria Portinari, who had purchased one of the towers of the castle wall, asked permission to be able to lower it by a few meters. In this case, as well, we bear witness to the progressive diminishment of functionality of the castle defenses. Today, in fact, there is no trace of the castle of Monterappoli as Leonardo saw it, with the exception of some ruins we can see near the church of San Lorenzo, and the nearby street by the name Via del Castello.