Pontoise. Pontoise is a commune in the northwestern suburbs of Paris, France. It is located 28.4 km from the centre of Paris, in the new town of Cergy-Pontoise. Pontoise is the official préfecture of the Val-d'Oise département, although in reality the préfecture building and administration, as well as the department council, are located in the neighboring commune of Cergy, which is regarded as the de facto capital of Val-d'Oise. Pontoise is also the seat of the Arrondissement of Pontoise. The sous-préfecture building and administration, unlike the préfecture, are located inside the commune of Pontoise. The city of Pontoise has three sister city relationships with: Böblingen since 1956;. Sevenoaks since 1964;. Geleen since 1962. Known for being a violent city in the late 20th century, with a criminal rate of 137.62 incidents per 1000 inhabitants, Cergy-Pontoise has enjoyed a significant decrease in violence in the first decade of the 21st century. By 2008, the rate had declined to 99.87, although this is still considered high. That rate has continued to decline in the second decade. Pontoise is the historical capital of the Vexin français. Its foundation dates from Roman times. At that time, the rock peak overhanging the river Oise supported the defense of the fort which was on the Roman road, the Chaussée Jules César, between Lutetia and Rotomagus. The road still exists and is now part of the N14 from Paris to Rouen. It is also known to many people as the birthplace of the alchemist Nicholas Flamel.With an over 2,000 year legacy, Pontoise still has vestiges of the past, such as medieval lanes, convents, churches and museums, and was awarded the City of Art and History Label in 2006.The impressionist painter Camille Pissarro made it famous through many paintings which are present nowadays in the most famous art galleries in the world.