Laon (anc. Lugdunum Clavatum, and Bibrax Suessonum; mediaeval Lat. Laudunum), a fortified city of France, capital of the department of Aisne, 74 m. N. E. of Paris; pop. in 1872, 10,268. It is mainly built on a steep isolated hill shaped like a V, and thought by many to be the Mons Bibrax mentioned by Ca3sar. On one arm of the V stand the modern citadel and the city proper enclosed by old fortifications; on the other is a Jesuit residence, the remaining portion of the once magnificent monastery of St. Vincent. Of the populous suburbs which once extended all round the foot of the mountain, only two small villages now remain. The cathedral was burned about 1112, and rebuilt in 1114. It formerly had six towers and a central dome over the transept, of which only the two western towers and one at the S. E. angle of the transept remain entire. The western front has recently been restored at an expense of 2,000,000 francs. Of the four other churches within the walls, two are also of the 12th century, one being a church of the knights templars. The city has a library of 20,000 volumes, with a collection of more than 2,000 rare autographs, a museum filled with Gallo-Roman and Celtic antiquities, a communal college, and a normal school.

It is an emporium for the manufactures of St. Quentin, St. Gobain, and Folen-bray; and has an active trade in nails, hats, woollen stuffs, and hosiery, besides corn, white poppy oil, and garden stuffs. In the suburbs are thriving potteries, tan yards, lime kilns, rope walks, and a manufactory of copperas. - Laon became the residence of Queen Brune-haut in 575, and the French kings frequently resided there till the accession of the house of Capet in 987. It has a famous school, in which Anselm of Canterbury and Abelard taught for some time. During the middle ages the burgesses maintained a long and bloody struggle for communal rights with the bishop and chapter. Since the time of Caesar Laon has sustained many sieges. It held out against Henry IV. in 1590, but was taken by him in 1594; was alternately occupied by the allies and Napoleon in 1814 and 1815, its environs being the scene of important engagements in March of the former year (see Butcher, vol. ii., pp. 755-6); and on Sept. 9, 1870, capitulated to the Germans. On the last occasion, just as the German troops were marching in, a French soldier blew up the powder magazine, killing and wounding several hundred persons.