Explicit reference to the castle is first made in 1150, when it is said that the Counts of Savoy controlled it, having acquired the rights to it, or sharing them with the sires of Blonay. As a result, they also controlled the route along the shores of the lake. In this document, Chillon is referred to as a castrum: given the mediaeval meaning of the word, this proves that there was a settlement associated with it. During the 13th century, the Counts of Savoy conquered most of the territory of Vaud, divided as it was into a number of small seigneuries. This marked the beginning of Savoy domination over approximately two-thirds of the territory which makes up today’s French-speaking Switzerland.
The land which they had conquered lay both to the north and to the south of the Alps, and they controlled the two major routes across the western Alps, namely the Mont Cenis Pass and the Great Saint Bernard Pass. These two passes, major trade routes which connect Italy with north-western Europe, proved to be a useful source of income. The upkeep of the roads and the protection offered to travellers were offset by the taxes levied on the goods transported across the territory. Because of its position on the second route, the castle was interesting for both economic and strategic reasons. In 1214, Thomas I of Savoy founded the town of Villeneuve, two kilometres above the bourg of Chillon, on a site which was large enough for the construction of a tollbooth, warehouses for the storage of goods and port facilities.