CHÂTEAUDUN, a town of France, capital formerly of the countship of Dunois, and now of an arrondissement in the department of Eure-et-Loir, 28 miles S.S.W. of Chartres. It stands on an eminence near the left bank of the Loir, and has remains of an old castle, several ancient churches, a town-hall, a communal college, a public library, and manufactures of woollens and leather. It was almost entirely destroyed by fire in 1723, and in 1870 it was captured by the Germans. Population in 1872, 5923.