The ancient castrum of the Obertenghi, perhaps dating back to the first Lombard inhabitants of the seventh century, was the first defensive settlement of Monterosso. Probably used by local lords such as the Lagneto, it was the Republic of Genoa at the beginning of the 13th century that fortified the village to protect it from Saracen raids. After a brief dispute with Pisa, the castle of Monterosso returned in 1254 to Genoa.
The Genoese defensive system was impressive. In the sixteenth century, in addition to the castle, it came to include thirteen towers and a curtain wall, of which remains today the current bell tower of the church of San Giovanni Battista, an ancient watchtower, the Aurora tower, located at the foot of the San Cristoforo hill, under the castle and a tower near the statue of the Giant.
Today the castle, overlooking the sea, has almost completely disappeared and is used as a municipal cemetery. Three towers remain in ruins, sections of walls with some battlements, remains of the citadel.