or SAARLOUYS, the frontier fortress of Prussia towards France, on the left bank of the Saar, in the province of the Rhine, government and 43 miles S. of Trèves. It occupies a peninsula formed by the river, and is strongly fortified; the works were constructed by Vauban in 1681, in the course of one year. There are a Protestant and a Roman Catholic church, a synagogue, hospital, school, barracks, &c. Linen cloth, leather, hardware, and fire-arms are made here; and there is some river navigation. Saarlouis is the birth-place of Marshal Ney, and the house where he was born is marked by a marble tablet. The name of the town, then in the possession of France, was changed to Sarreilire at the time of the first revolution. It was ceded to Prussia in 1815. Pop. 6340.