This is a small town dominated by the Maritime Alps on the border with Piedmont; it was a "castrum" in Roman times and called "Castellania Cuxii" in the Middle Ages, which is where its name derives from. During the decline of the Western Empire, Castrum Cuxii was fortified with a tower, which is today the oratory bell tower. It belonged to the Clavesana family and then to Genoa from 1274 until the Napoleonic era.
The compact town has two faces: on the one hand there is the underground layout of the maze of dark alleys and tunnels; on the other hand, there are the low sunlit houses, with balconies so close together that they almost touch, and the characteristic slate roofs. Cosio was not affected by the building boom, although it has felt the effects of depopulation.
The fine arts and monuments authority has promoted many initiatives for the restoration of the ancient houses and general recovery of the territory. Of particular importance is the restoration of the oratory of Nostra Signora Assunta, a national monument and the original nucleus around which the town developed in mediaeval times. The bell tower of the oratory, with its fourteenth-century brickwork mullioned windows and small marble columns, rises out above the rooftops. Extended in the late Baroque period, it now forms part of the town hall building.
Besides being popular for fishing and hunting, Cosio is also a favourite place for Sunday outings because of the fresh mountain air, the delicious food (including a speciality called "pizzoccheri" and ravioli with herbs and potatoes) and the many opportunities for making excursions. Among the interesting places to visit are the fort on Monte Esce, the Cornarena grotto and Colletta in the Cosio countryside.
