Orsay (French pronunciation: [ɔʁsɛ]) is a commune in the Essonne department in Île-de-France in northern France. It is located in the southwestern suburbs of Paris, France, 20.7 km (12.9 mi) from the centre of Paris. A fortified location of the Chevreuse valley since the 8th century and agricultural domain of wealthy and influential people, the development of Orsay is marked by the introduction of a railroad in the second half of the 18th century (today the RER B of which two stations are located in Orsay) and donations which allow the construction of a hospital still active to this day.