AAR or AARE, the largest river entirely within Switzerland. It rises in the great Aar glaciers, in the canton of Berne, west of the Grimsel pass. Beyond the Handegg waterfall the river traverses the Hasli Thal and expands into the Lake of Brienz, where it becomes navigable. It then crosses the swampy plain of the &deli, between Interlaken (left) and Unterseen (right), be fore again expanding into the Lake of Thun. Running north north-west it encircles the lofty bluff on which the town of Berne is built, and then turns west, and later north. Near Aarberg its stream is diverted west by the Hagneck canal into the Lake of Bienne whence the Nidau canal runs east to Bilren. Henceforth its long north-east valley drains the central lowland of north Switzer land, parallel to the Jura. The chief tributaries in this stretch are the Grosse Emme, Wigger, Suhr and Aa, all from the right. Below Brugg it receives first the Reuss, and then the Limmat or Linth. It now turns due north, and soon becomes itself an affluent of the Rhine (left), which it surpasses in volume when they unite at Coblenz, opposite Waldshut. Length of river, 181m. Area of basin, 6,8o4sq.m.