Besançon is an old city. It is discovered in 58 BC and Julius Caesar writes about it in his book Commentarii de Bello Gallico where it is called "Vesontio". The etymology (origin of the word) is not certain. It could have a Celtic origin. The Celtic word "wes" means mountain. In the 4th century, the letter B became V. The city name changed to "Besontio" or "Bisontion". It became Besançon in 1243. In 1871 the city is going through a revolutionary period, known as Besançon Commune.