The Castle Hill of Grosio is dominated by two castles. The Old Castle (Castello Vecchio) was probably built at the end of the 10th century. The Castello Nuovo was built as a stronghold between 1350 and 1375 due to the military-strategic needs of the 14th century.
The castle is surrounded by a double defense wall and had next to e solid keep even a fortified internal tower. Apart from a military expedition by Giovanni Cane in 1376 to Bormio, which had its starting point here, the Castello Nuovo was never involved in military confrontation or siege. Today the castle is only preserved as a castle ruin because after 1526 the new political power in Valtellina ordered the destruction of all fortifications in the valley. That way the dominion of the Three Leagues wanted to avoid any potential danger that could emanate from their own castles.
During the period of the Bündner Wirren (1620-1639), the Thirty Years' War in Europe, the structure was used by the French under Duke Rohan as a military base and got partially restored. The Castello Nuovo is nowadays the best-preserved example of all the historic defensive structures in the Valtellina.
Between 1992 and 1997 in the area of the Castello Nuovo archaeological excavations could document the remains of a bronze and iron age settlement, dating from the middle of the 2nd to the end of the 1st millennium BC. Some of the small finds are now exposed in the excavation museum.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.