Regional Natural Monument of Preia Buia, Natural monument in Sesto Calende, Italy.
The Preia Buia natural monument is a megalithic complex centred on a large erratic boulder of serpentinite, a greenish sparkling rock, with two smaller erratic boulders beside it. All three bear prehistoric petroglyphs and cup marks. The main boulder rises as a broad, uneven wall of dark grey and charcoal, cut by horizontal cracks and shallow ledges, with faded blue and red paint marks on its lower face. It stands in woodland about a hundred metres north of the Oratory of San Vincenzo.
The boulders were transported to this location during the last glaciation of the Quaternary period by moving ice sheets. The carved symbols on the rocks demonstrate that people used this site for rituals during prehistoric times.
Local tradition links the boulder to myths of motherhood and fertility, to Greek mythology, and to Saint George and the Dragon. The petroglyphs and cup marks suggest the site served as a prehistoric altar, and the two smaller engraved boulders stand beside it.
The site is part of the Ticino Valley Natural Park and is reachable on foot via local hiking trails. Visit with sturdy footwear since the ground can be uneven and damp due to the wooded surroundings.
The serpentinite does not occur naturally in the hills above Sesto Calende; it was carried here by Quaternary glaciers, which is why the boulder sits in a wooded morainic area. The same ice sheets left the surrounding moraine deposits across the Lombard Prealps.
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