Towards the end of the 10th century, Rodolphe Aynard had a castrum built in his seigneury of Theys. The Latin term castrum designates different realities ranging from a fortified tower on a motte castrale to a fortified town. We do not know the location of this primitive castrum, of which no traces seem to remain.

On the other hand, when, from the 1280s onwards, the Count of Geneva, the new lord of Theys, established his stronghold at the place known as “Au Châtel”, He locked the esplanade naturally protected by two deep streams by raising a motte topped by a stone tower upstream, at the most constricted point. This is a procedure that is well known in the Geneva region and which continued until the 14th century.

It is therefore necessary to distinguish this type of fortification, which works in conjunction with a dry ditch downstream, from a motte castrale as was built in the 10th and 11th centuries and which perhaps corresponds to what the texts refer to as a castrum when they describe the fortification built by Rodolphe Aynard.