This project began in 1997 as part of a larger study on Tuscan medieval landscapes under the direction of Riccardo Francovich, but extended its research aims to include the development and transformation of the castles until the end of the Middle Ages. The excavation is ongoing and so far has covered just over 20% of the total surface area. At present the site shows evidence of Bronze Age occupation, a substantial Etruscan phase, faint traces of the late antique and again evidence for substantial occupation in the full and late medieval periods.

Although not much prehistoric material was found at Castel di Pietra it is of great interest. It dates the first occupation to the late Bronze Age and early Iron Age, which throughout Etruria corresponds with the crucial moment that saw the development of a process of political and territorial reorganisation with the birth of the large proto-urban centres on the plains where the Etruscan cities would stand. Also of great interest is the fact that parallels with the prehistoric pottery from Castel di Pietra are found in coeval settlements that are mainly in northern Tuscany rather than the closer south Etruria.

The earliest Etruscan evidence (end of the 7th-beginning of the 6th century) was a monumental terracing wall constructed in order to contain the upper and easternmost part of the plateau. Here, the remains of a building, two cisterns and other structures relating to craft working activities were uncovered. The site was abandoned around the mid 5th century B.C., when the Syracusan expedition along the Etruscan coast hit Vetulonia and its territory. Towards the end of the 4th century B.C. the plateau was reoccupied, including its western part. Between the 3rd and 2nd century B.C. at least two residential and productive complexes were built, each associated with opus signinum tanks, whilst the large cisterns from the preceding period remained in use. The Hellenistic site at Castel di Pietra on the one hand attests the necessity for a fortress, a site controlling the roads and perhaps also the mineral resources, on the other hand a resumption of agricultural activity. The lack of archaeological data for the 1st century B.C. attests the end of occupation on the hill at the beginning of the century, when the civil war between Marius and Sulla devastated this area.

Evidence for the late antique and early medieval phase was scarce, comprising fragments of walls and pottery, often in secondary deposition.
Contemporary with the first documentary attestations there was evidence of a trapezoidal tower, abutted by a second square tower and sections of a curtain wall which seemed to shape the landscape of the Rocca di Pietra cited in 1049 to the castellum de Petra cited in 1104. The castle was restructured and enlarged about a century later, with the enclosure of the keep, the curtain wall visible today (enclosing an area double the earlier one) and perhaps that of the plateau below. The passage from the Aldobrandeschi to the Pannocchieschi family determined a series of construction phases in rapid succession between the full 13th and the mid 14th century (enlargement and reconstruction of buildings, defensive walls, an aristocratic palace) making wide use of brick. The second half of the 14th century and first decades of the 15th century was a period of radical transformations in the urban layout of Pietra, attesting the weakening of aristocratic power (division of the keep into two separate dwellings, substantial reuse of materials, advanced state of degradation of some buildings, open air middens and hearths).