Some historians claim that a fortification already existed on thg site of Castel Selva in proto-historic times, which was part of the defence system of the Roman Via Claudia Augusta road. Other academics maintain that the castle was built in late antiquity, as the Roman Empire waned orto defend the territory against Hungarian raids in the 9th Century.
For the time being, at least, the earliest existing documentation of the Castrum silue (Castel Selva) dates to the beginning of the 13th Century: the castle was the alodium (property, in the broad sense of the term) of the Bishop Salomone, and was enfeoffed to Corradino da Caldonazzo. This document also contains valuable references to the structure of the Castrum, hinting at the existence of a curtain (presumably in stone) and stating that there was a domus inside the castle, standing near a unum cassamentum -land destined for the construction of a building - reserved for the bishop. The fact that the castle contained a domus is indicative of its relatively advanced status, whereas the subdivided land demonstrates that this was a somewhat complex structure. Other details of the castle may be deduced from a decree registering a dispute occurring in 1224: for instance the 'casa'
(house) is now referred to as 'maggiore' (main house), whereas the area to the south was occupied by a Cassaturem, perhaps a tower house. At this point the perimeter wall still enclosed only a few buildings, with an empty space destined - to the south at least-to be filled with future fortification structures or elements. As it stood and in its strategic position, the castle complex undoubtedly controlled access through the valley and, in the event of major war, could also be included in a defence system together with the Colle di Brenta and Vigolo Vattaro castles. This was a common arrangement among the fortifications in the Valsugana area during the Late Middle Ages