REICHENAU a picturesque island in the Untersee or western arm of the lake of Constance, is 3 miles in length by 1 in breadth, and is connected with the east bank by a causeway three quarters of a mile long. It belongs to the duchy of Baden, and comprises the three parishes of Ober-zell, Mittelzell, and Unterzell, with a joint population of 1463 in 1880. The soil is very fertile, and excellent wine is produced in sufficient quantity for exportation. The Benedictine abbey of Reichenau, founded in 724, was long celebrated for its wealth and for the services rendered by its monks to the cause of learning. In 1538 the abbey, which had previously been independent, was subordinated to the see of Constance, and in 1799 it was secularized. The abbey church, dating in part from the 9th century, contains the tomb of Charles the Fat, who retired to this island in 887, after losing the empire of Charlemagne. It now serves as the parish church of Mittelzell, and the churches of Oberzell and Unterzell are also interesting buildings of the Carlovingian era.