Chaumont (shōmōNˈ) [key], town (1990 pop. 28,900), capital of Haute-Marne dept., NE France, in Champagne, at the confluence of the Marne and Saize rivers. It is a railroad and light industrial center. Iron is mined nearby. The Treaty of Chaumont, signed on Mar. 1, 1814, by England, Russia, Prussia, and Austria, laid the foundation for the Holy Alliance.