From the sources it is known that in the early medieval period the curtis of Castagneto was situated in this territory and may perhaps be identified with the modern town. In the mid 8th century it was donated by the Pisan noble Valfredo to the nearby monastery of S. Pietro Monteverdi, of which he was one of the founders.

The excavation revealed that its origins date back to the Hellenistic period when it may have been an outpost on the northern border of the ager Populoniensis, defending the coast and the mining district in the interior. The settlement retained its strategic importance under Roman domination, with continuous occupation between the Republican and late antique periods.

The available data suggests that the summit was re-occupied between the 6th and 7th century, whilst the evidence of the 8th century wooden settlement is more certain. The latter is attested by two circular huts situated in the southern part of the borgo, the zone where the archaeological evidence was best preserved from the late medieval destruction of the summit area for the construction of aristocratic residences.

In the second half of the 9th century the first stone defensive wall and a church on the summit plateau were built. A dividing wall was also built in the borgo, which in the eastern part enclosed the only point where water was available, constituted by a well, probably dating to the Hellenistic period, surrounded by wooden structures. The settlement, constituted by wooden huts, underwent alterations until the end of the 11th century, these were identified both in the area of the borgo and in the flat zones below the summit.(MiBAC)