The Castle Hill have a mix of the historical, archaeological, architectural and natural patrimony of various ages of the Valtellina. The hill is dominated by two castles. The “Castello Vecchio” (Old Castle) from the 10th-11th century and the “Castello Nuovo” (New Castle) which got constructed in the 14th century. Is interesting too, the traditional system of dry-stone terraces surrounding the hill, and unique is the “Rupe Magna”, a large rock which contains more than 5,000 engraved figures from the 4th to the 1st millennium BC. The “Castello Vecchio” (Old Castle) was mentioned the first time in a written document in the year of 1150 like „Castrum Groxi“, but archaeological results says about a construction date already at about the end of the 10th century. The preserved walls of this castle show all the historic size of the structure. The dominating church spire since Romanesque Period was partly restructured at the end of the 19th century. The first phase of construction of the corresponding small church is dated by archaeological results into the 7th or 8th century, most probably built to cover the two medieval tombs which are cut directly into the rock. The small size as well as the low fortification level indicate, that the castle was more a symbol of power of the feudatory than a fortress. The feudatories of this area of the Valtellina were at this historic age the bishops of Como. Since the 12th century their vassals in the region of Grosio were the lords von Matsch, a family originars from Vinschgau (the italian “Val Venosta”). According to historic documents, the castle was inhabited until the last decades of the 16th century.
Instead, the New Castle (Castello Nuovo) was built between 1350 and 1375 on the initiative of the House of Visconti. The Visconti family, already lords of Milan, in 1335 acquired also the region of Valtellina, after defeating the commune of Como. The new castle was designed as a stronghold, adapted to the strategic needs of the 14th century. It was surrounded by a double defensive wall, had a solid keep and a fortified internal tower (Bergfried) as an ultimate defense structure. The southern part of the castle is built directly of the Castle Hill, while the northern part had a moat. Nevertheless, the fortress was never involved into fighting action. As early as in 1526 the New Castle was partially demolished by the new lords of the Valtellina to avoid possibilities of any kind of insurrection. Some years before, in 1512, the three counties Chiavenna, Valtellina and Bormio became part of the Three Leages (the Grisons) with the status of a subordinated land.