​ST DIZIER, a town of north-eastern France, in the department of Haute-Marne, 45 m. N.N.W. of Chaumont by rail, on the Marne and the Haute-Marne canal. Pop. (1906) town, 10,316; commune, 14,661. The town is a very important centre of the iron trade, with foundries, forges and engineering ​works, and has trade in grain and timber. It dates from the 3rd century, when the relics of Bishop St Didier (whence the name of the town) were brought thither after the destruction of Langres by the Germans. It sustained a memorable siege against Charles V. in 1544.