ALLIER (anc. Slaver)  , a river of central France flowing into the Loire . It rises in the department of Lozere, among the Margeride mountains, a few miles east of the town of Mende . The upper course of the Allier separates the mountains of the Margeride from those of the Velay and lies for the most part through deep gorges . The river then traverses the plains of Langeac and Brioude, and receives the waters of the Alagnon some miles above the town of Issoire . Swelled by torrents from the mountains of Dore and Dome, it unites with the river Dore at its entrance to the department to which it gives its name . It then flows through a wide but shallow channel, joining the Sioule some distance above Moulins, the chief town on its banks . It soon after becomes the boundary line between the departments of Cher and Nievre, and reaches the Loire 4 m. west of Nevers, after a course of 269 M . Its basin has an area. of 6755 sq. m . The Allier is classed as navigable for the last 154 M. of its course, but there is little traffic on it .