Vaud is the third largest of Swiss cantons by population and fourth by size. It is located in Romandie, the French-speaking western part of the country, and borders the canton of Neuchâtel to the north, the cantons of Fribourg and Bern to the east, Valais and Lake Geneva to the south, the canton of Geneva to the south-west and France to the west.
Along the lakes, Vaud was inhabited in prehistoric times. Later, the Celtic tribe of the Helvetii inhabited the area. The tribe was defeated by Caesar's troops in 58 BC and as a consequence the Romans settled the area. The towns of Vevey and Lausanne (Lausonium or Lausonna) are two of the many towns established by the Romans.
In 27 BC the state of Civitas Helvetiorum was established around the capital of Avenches (Aventicum). There are still many Roman remains around the town today. Between the 2nd and the 4th century the area was repeatedly invaded by Alemannic tribes, and in the 5th century the Burgundians occupied the area. The Merovingian Franks later replaced the Burgundians. Their occupancy did not last long either, and in 888 the area of the canton of Vaud was made part of the Carolingian Empire. In 1032 the Zähringens of Germany defeated the Burgundians. The Zähringens themselves were succeeded in 1218 by the counts of Savoy. It was only under the counts of Savoy that the area was given political unity, establishing the Barony of Vaud. A part stretching from Attalens to the River Sarine, in the north, was absorbed by the canton of Fribourg.
The Bernese occupants were not popular amongst the population. In 1723, Major Abraham Davel led a revolt against Bern, in protest at what he saw as the denial of political rights of the French-speaking Vaudois by the German-speaking Bernese, and was subsequently beheaded. Later, inspired by the French Revolution, the Vaudois drove out the Bernese governor in 1798 and declared the Lemanic Republic. Vaud nationalists like Frédéric-César de La Harpe had called for French intervention in liberating the area and French Revolutionary troops moved in, taking over the whole of Switzerland itself in the process and setting up the Helvetic Republic. Under Napoleon I, it became the canton of Léman. Unrest about the abolition of feudal rights and taxes led to increased discontent, which culminated in the revolt of the Bourla-papey in Spring 1802, closely followed by the Stecklikrieg that brought the end of the entire Helvetic Republic. In 1803, Vaud joined the re-installed Swiss confederation. In spite of Bernese attempts to reclaim Vaud, it has remained a sovereign canton ever since.
In the 19th century, the canton of Vaud was an outspoken opponent of the Sonderbund Catholic separatist movement, which led to intervention in 1847 by 99,000 Swiss Federal troops under General Henri Dufour against 79,000 separatists, in what is called the Sonderbund War. Separation was prevented at the cost of very few lives. The current constitution dates from 14 April 2003, replacing the one from 1885.