The castle of Saint-Germain was built between the 11th and 12th centuries by the De Mongioveto family, probably to control the road below and to convince travellers to pay them a toll. The central keep and a first circle of walls date back to this period, perhaps on a pre-existing structure. In particular, Feidino De Mongioveto seems to have been particularly tenacious and oppressive in demanding the toll, to the point that the Duke of Savoy had the pretext to take over the fortress. The castle did not remain in the Savoy family for long. The fief of Montjovet, and therefore the castle, witnessed the rise of the Challants when in 1295 it became the property of the family. Francesco di Challant, advisor to Duke Amedeo VIII of Savoy, brought the castle back into Savoyard hands in 1438, ceding the castellany of Montjovet with the castle, the lands and the village. Amadeus VIII and his successors contributed to making the castle increasingly efficient by updating it to new military techniques. The new city walls, battery positions, turrets and cannon positions date back to this period. In 1661 the castle was abandoned and artfully demolished to prevent foreign troops from stationing there, at the behest of Charles Emmanuel II of Savoy, while the garrison was transferred to the fort of Bard. At the beginning of the 18th century it finally fell into ruin. Today the castle of Saint-Germain is owned by the Aosta Valley Region.