The birth of the castle of Carrosio, located on the rock overlooking the Lemme river, is due to the marquises of Gavi who, around the second half of the 12th century, decided to build a fortification to watch over the advance of Genoese soldiers and rob the Ligurian merchants . The Genoa response was not slow to arrive: in 1197 the castle was, in fact, destroyed by the Genoese who, after having taken over Carrosio, rebuilt it in the same position. The definitive end of the fortification dates back to the 14th century when the Genoese Republic forcibly suppressed popular dissent and destroyed the small fortress that was no longer rebuilt. A part of the walls and a lookout tower survive from the ancient structure, still clearly visible from the river, while the secret passages that brought the feudal lord's palace into contact with the castle and the latter with the river bank are no longer accessible. below.