Among fortification works in the area of Alta Valtellina, the Fraele Towers are the most striking and historically important ones.

Built at an altitude of 1,941 meters, at the entrance of the Valley of Fraele, to guard the Scale Pass, represented a strategic stronghold to defend the County of Bormio. The two towers, the only ones in the Province of Sondrio built to control a pass, watched over much of the Magnificent Land supervising, one on each side, the old "Imperial Way of Alemagna" that, through the pass, ensured communications between Bormio, Livigno, Valley Monastery and Tyrol.

Fraele Towers were built in 1391 in the midst of the Visconti period, although in the tradition they are commonly referred to as "Roman". Even though the structures are of the middle ages, it is legitimate to think that may have been rebuilt several times over the centuries, overlapping the works that already in ancient times protected the pass. Their strategic importance is demonstrated by the construction of a fortification in 1481 by the Duke of Milan, Ludovico il Moro, who established ten soldiers in the garrison.

During the reign of the Sforza, the towers were the scene of the decisive battle between the troops of the County of Bormio and those of the invaders from the federation of the three Grey Leagues, who had rights in the territory of Alta Valtellina. The defense of Bormio was strenuous, but not sufficient to prevent the entry of Grisons in the country, after a bloody battle at Scale Pass. Here riders and horses of the invading army found their way interrupted on the ravine, which, from the threshold of the valley - manned by the famous towers - falls on the plain of Prada, upstream of Pedenosso, and with the favour of darkness and deception, were induced to fall into the ravine below, which remains in popular memory with the name of "Canyon of the Dead." Over the following decades the place was the scene of other historical military clashes and the towers were damaged by the invading Grisons in the early decades of the '500 and progressively dismantled

The ruins hanging over up to the present day are all that remains of the military outpost, although a recent restructuring has allowed the reconstruction of the west tower, which is the best preserved and measures about m. 6.50 per side, with a height of over 13 meters. This tower had the original entrance on the first floor, where access was possible via a retractable ladder, while the current opening on the ground floor is subsequent and leads into a room with a fireplace. The upper floors are reached via a wooden staircase of recent construction. The second tower, to the east, like the first, has thick walls and a square of side m. 5.75, but is missing many of its parts, in particular the western wall.