ALLIER, a department of France on the northern border of the Massif Central, formed in 1 790 from the old province of Bourbonnais. Area 2,848sq.m. Pop. (1931) 373,924, a consider able decrease since 1906. It is bounded on the north by Nievre, east by Saone-et-Loire, south-east by Loire, south by Puy-de Dome, south-west by Creuse, and north-west by Cher. The de partment is a well watered plateau, mostly 600–I,5ooft. above sea level, with heights reaching 4,239ft. in the south, in the Bois Noirs, and forests in the northern zone. The Allier crosses the centre from south to north, the Loire forms most of the eastern boundary, and the Cher runs parallel to the Allier across the west. The heights of the Forez in the south-east and beyond get one metre of rain or more per annum and the mean winter tem perature (reduced to sea level) is 39°, implying severe conditions on the heights. In the lower lands the rainfall is 600-800mm. per annum. The basin of the Allier east of its tributary the Sioule, within the department, is largely a northward continuation of the fertile Limagne of the Allier valley in Puy-de-Dome, and is called the Limagne Bourbonnaise. It grows cereals, potatoes, and fruits, including some vines. Sheep and cattle rearing is active in the department and goats and pigs are numerous, while there are also several forests.
Carboniferous rocks outcrop along north-east to south-west lines west of the Allier, with coal seams worked for the iron and other industries at Montlucon, Commentry, Murat, etc. There are also lime and building stone quarries, so that the mineral wealth is considerable. The mineral waters of the region are widely famed, Vichy (q.v.), in the arrondissement de la Palisse, being the best known spa in France.
Allier is served chiefly by the Orleans and P.L.M. railways and the lateral Loire canal; the Berry canal and the canal from Roanne to Digoin touch the department. Moulins (the capital), Montlucon and Lapalisse are towns which give their names to the usual three arrondissements of the modern system. There are 29 cantons and 321 communes. The department is also the diocese of Moulins under the archbishop of Bourges. It is in the region of the XIII. army corps and in the academie or educational province of Clermont Ferrand. Its court of appeal is at Riom.
Apart from Moulins (q.v.), it may be mentioned that the de partment has interesting mediaeval buildings at Souvigny (Cluniac priory 11th–I5th century), St. Menoux, Ebreuil, Gannat, Veauce and Ygrande (Romanesque churches), Huriel (fine Ilth century church, also castle), St. Pourcain sur Sioule (11th-18th century church). The castle at Bourbon 1'Archambault c13th–I5th cen tury) was the house of the Bourbon dukes.