The naming of the upper part of the village Castello (Castle) is explained by the presence of ruins of fortifications, in use up until the 18th century, in the form of walls and towers. Close to the remains of the tower, which has a pentagonal floor plan and once dominated a good part of the valley of the Lima, lies a pentagonal stone that was probably used as a solar calendar. Only the base of this tower, alongside which a small church was built in the 16th century, remains.
Also meaningful is the name given to the hamlet of little houses, or casulae, surrounding the fortress: from Casulae derives the name of the village, Casoli; as often happened in such situations, the name reflects a pattern typical of the early Middle Ages, with the dwellings placed around the highest, fortified area, which had been occupied earlier.
At the foot of a section of the ruins of the internal walls, we find an outcrop of whitish cavernous limestone in the form of two truncated cones, one on top of the other, whose upper, slightly sloping, surface is about a metre across.
Opposite this stone, to the South and a short distance from the beginning of the slope, we see a rocky outcrop, the nearest part of which has a semi-circular cross-section.
This second outcrop has also been worked by man: two seats linked together have been identified facing the stone.
Scholars have identified the stone as an altar, while the outcrop is thought to have been a seat adjacent to it.
Along the side of the cone, not far from the upper surface, there are four holes which cannot be due to atmospheric erosion; and the presence here of man-made holes leads us to ask why the holes were made: the most convincing hypothesis is that this was an astronomical calendar, or rather that the stone in the form of two truncated cones made up the central element of such an instrument as used by ancient peoples such as Celts.
The holes would then correspond to the extremities of the Sun’s apparent orbit; they would therefore mark off the seasons and show when the appropriate rituals should be observed.
There is disagreement about the date of the monument.ThereOne theory dates the stone-calendar to the very distant past, before the 2nd century B.C., the work of Celtic-Ligurians.
Others have attributed it to more recent times, about the 6th-7th centuries A.D., when Irish monks arrived in the Lucca area.