Observation point: from the bottom of the valley, looking to its right flank 
 
At the southern margin of Grosio settlement, the Roasco creek turns suddenly toward the south before flowing into the Adda river, since its regular course is obstructed by a rounded hill made of strong metamorphic rocks, and smoothed by a Pleistocene glacier.  
A double ashlar stone curtain wall crowns it, with evident crenellated battlements: the best preserved castle of Sondrio province, was built here, at the strategic crossing between Grosina valley ancient road and the main route along Valtellina bottom, towards Bormio and South Tyrol. 
Coming from the south, the first elder building, known as Castrum Grosii, appears as an elongated ruined structure which fits the morphology of the hill: dating back to X or perhaps XI century, it was controlled by the bishop of Como, who was the great feudatory of this part of the valley. The internal organization is only partially clear: it appears very simple, with traces of some rectangular rooms and the foundations of a chapel: this latter is put in evidence by the restored bell-tower, but also the semicircular apse and two graves carved into the rock are well recognizable. 
The main castle, or Castrum Novum, stands on top of the hill, dominating all the valley; it was built between 1350 and 1375 by Bernabò Visconti, lord of Milan, during the offensive which led him to conquer Valtellina up to Bormio. Its gate opens on a large main bailey, with the remains of an isolated, rectangular donjon and a curtain with an imposing three-storey bastion. An external curtain was built on the southeaster slope in a second phase, delimitating a lower bailey and strengthening the whole fortification. 
Together with the other castles of Valtellina, Grosio one was greatly dismantled by the Grisons, who in 1512 conquered the upper valley, in order to prevent its use by local populations, during a possible revolt against them. 
After all, Grosio hill has been considered strategic since prehistoric times, because of its position on the main traffic routes through central alpine chain, being at the same time easy to defend; in the main bailey, indeed, archaeological digs have revealed a Middle-Later Bronze Age fortified settlement: perhaps the village of the mysterious authors of the majority of the unique engraving on the nearby rocks, which reflects in their features the regular connection of inhabitants with High Rhone valley and with Tyrol. 

• Website:
• https://www.parcoincisionigrosio.it/