At the beginning of the 13th century the small town of Castra was part of the territory dependent on the city of Pistoia. Its appearance in the municipal papers of that city dates back only to 1222, when, the homines de Castra were guilty of brigandage to the detriment of Florentine merchants. The event ended up in the public papers of the town of Pistoia, because it occurred in the context of war acts between the cities of Lucca and Pisa: the raids carried out by the men of Castra were sanctioned by Florence, then allied with Lucca against the Pisans; and the municipality of Pistoia, in whose district the incident occurred, had to ratify the restitution of the more than 700 squirrel skins taken from Florentine merchants. In the middle of the 13th century the Liberor Focorum—the register of the population of the circumscriptions of the district of Pistoia—reports, for the small rural town of Castra, a list of 41 "hearths", i. e., families residing in what must already have been a castle, or would, in any case, have become so within a short time. In the early 14th century, in fact, Castra is called Castrum Castri Vallis Arni, or "castle of Castra della Valle dell'Arno", while the nearby village of Conio is still defined as an open village (Villa Conii Vallis Arni). At that time, the boundary of the Pistoia district had come to include the castles of eastern Montalbano (Carmignano, Artimino, and Bacchereto) and the small castle of Castra, represented for some time one of the most tenacious cornerstones of the territory of that city. The road that, passing over the ridge of Montalbano, reaches Castra and then Castellina near Limite Sull'Arno, made it possible, among other things, to easily connect the city of Pistoia to the Lower Valdarno and the river.