Collescille is situated in the highest part of the Castoriana Valley, the name of which may be linked to the ancient character of Castorius, or according to other evocative hypotheses to the presence of an ancient cult dedicated to Castore and Polluce.

The small mountainous impluvium consists not only of Collescille, but also of the towns of Valle, Piedivalle and Acquaro (the four towns that made up the so-called “Guaita della Badia”). Already in the 11th century the entire Castoriana valley consisted of a considerably large fiefdom that included Acquaro, Collescille, Piedivalle, Casteldigrappa, Presenzano, Campi, Todiano and Collesecco.

The abbey of Sant’Eutizio was for a long time the important, cultural and economic centre of today’s Valnerina and received a considerable income in kind of both agricultural products (cereals, oil, cheese, as well as pepper and saffron) and manufactured goods (San Marco and San Pietro di Acquaro paid their census with plates, dishes and knives, San Lorenzo di Canatra-Castelluccio with glasses). The local production was not only able to satisfy the needs of the local people, it also traded with Rome and probably even further afield, as some of the goods found do not originally come from that area.

Collescille, or villa Collescille, thanks to its dominant position over the valley below and to the presence of a tower, represented an important stronghold that was not easily conquerable. Ciucci recalls the village under the name of Toccalomò. At the beginning of the 13th century it was one of the independent fortresses subject to the tax of the fodrum.