Chillon Castle (French: Château de Chillon) is an island castle located on Lake Geneva (Lac Léman), south of Veytaux in the canton of Vaud. It is situated at the eastern end of the lake, on the narrow shore between Montreux and Villeneuve, which gives access to the Alpine valley of the Rhône. Chillon is amongst the most visited medieval castles in Switzerland and Europe. Successively occupied by the house of Savoy then by the Bernese from 1536 until 1798, it now belongs to the State of Vaud and is classified as a Swiss Cultural Property of National Significance. The Fort de Chillon, its modern counterpart, is hidden on the steep side of the mountain.

According to the Swiss ethnologist Albert Samuel Gatschet, the name Chillon derives from the Waldensian dialect and means "flat stone, slab, platform". The name Castrum Quilonis, attested from 1195, would, therefore, mean "castle built on a rock platform.

Chillon began as a Roman outpost, guarding the strategic road through the Alpine passes. Objects dating back to Roman times were discovered during excavations in the 19th century, as well as remains from the Bronze Age. From a double wooden palisade, the Romans would have fortified the site before a square donjon was added in the 10th century. Sources from the 13th century link the possession of the Chillon site to the Bishop of Sion.

The oldest parts of the castle have not been dated definitively, but the first written record of the castle was in 1005. It was built to control the road from Burgundy to the Great Saint Bernard Pass. A charter of 1150, in which Count Humbert III granted the Cistercians of Hautcrêt free passage to Chillon, names the owner of the castle as Gaucher de Blonay, a vassal of the Count of Savoy within the feudal society of the time.

From the mid 12th century, the castle was summer home to the Counts of Savoy, who kept a fleet of ships on Lake Geneva. The castle was greatly expanded in 1248 and 1266-7 by Count Peter II. During this time the distinctive windows were added by Master James of Saint George, who is believed also to have added similar windows to Harlech Castle in Wales at a later date.

During the 16th century Wars of Religion, the dukes of Savoy used the castle to house prisoners. Its most famous prisoner was probably François de Bonivard, a Genevois monk, prior to St. Victor in Geneva and politician, who was imprisoned there in 1530 for defending his homeland from the dukes of Savoy. Over his six-year term, de Bonivard paced as far as his chain would allow, and the chain and rut are still visible.

In 1536 the castle was captured by a Genevois and Bernese force and all the prisoners, including de Bonivard, were released. The castle became the residence for the Bernese bailiff until Chillon was converted into a state prison in 1733.

In 1798, the French-speaking canton of Vaud drove out the German-speaking Bernese authorities and declared the Lemanic Republic. The Vaudois invited in French troops to help them maintain autonomy from the other Swiss. When the French moved in and occupied, Chillon was used as a munitions and weapons depot.

From the end of the 18th century, the castle attracted romantic writers and inspired poets from around the world, including Jean-Jacques Rousseau, Victor Hugo, Alexandre Dumas, Gustave Flaubert and Lord Byron. By 1939, helped by its proximity to the popular tourist destination Montreux, the castle was attracting over 100,000 visitors a year. By 2005, this number had increased to 300,000.^[19]

Chillon remains open to the public for visits and tours on an entrance fee basis and is, according to the castle's website, "Switzerland's most visited historic monument". There are parking spaces and a nearby bus stop. Inside the castle are recreations of the interiors of some of the main rooms including the grand bedroom, hall, and cave stores. Visitors can view four great halls, three courtyards, and a series of bedrooms including the Camera domini, which was occupied by the Duke of Savoy and is decorated with 14th-century murals.