HIRSAU (formerly _Hirschau_), a village of Germany, in the kingdom of Wurttemberg, on the Nagold and the Pforzheim-Horb railway, 2 m. N. of Calw. Pop. 800. Hirsau has some small manufactures, but it owes its origin and historical interest to its former Benedictine monastery, _Monasterium Hirsaugiense_, at one period one of the most famous in Europe. Its picturesque ruins, of which only the chapel with the library hall are still in good preservation, testify to the pristine grandeur of the establishment. It was founded about 830 by Count Erlafried of Calw, at the instigation of his son, Bishop Notting of Vercelli, who enriched it with, among other treasures, the body of St Aurelius. Its first occupants (838) were a colony of fifteen monks from Fulda, disciples of Hrabanus Maurus and Walafrid Strabo, headed by the abbot Liudebert. During about a century and a half, under the fostering care of the counts of Calw, it enjoyed great prosperity, and became an important seat of learning; but towards the end of the 10th century the ravages of the pestilence combined with the rapacity of its patrons, and the selfishness and immorality of its inmates, to bring it to the lowest ebb. After it had been desolate and in ruins for upwards of sixty years it was rebuilt in 1059, and under Abbot William--Wilhelm von Hirsau--abbot from 1069 to 1091, it more than regained its former splendour. By his _Constitutiones Hirsaugienses_, a new religious order, the Ordo Hirsaugiensis, was formed, the rule of which was afterwards adopted by many monastic establishments throughout Germany, such as those of Blaubeuren, Erfurt and Schaffhausen. The friend and correspondent of Pope Gregory VII., and of Anselm of Canterbury, Abbot William took active part in the politico-ecclesiastical controversies of his time; while a treatise from his pen, _De musica et tonis_, as well as the _Philosophicarum et astronomicarum institutionum libri iii._, bears witness to his interest in science and philosophy. About the end of the 12th century the material and moral welfare of Hirsau was again very perceptibly on the decline; and it never afterwards again rose into importance. In consequence of the Reformation it was secularized in 1558; in 1692 it was laid in ruins by the French. The _Chronicon Hirsaugiense_, or, as in the later edition it is called, _Annales Hirsaugienses_ of Abbot Trithemius (Basel, 1559; St Gall, 1690), is, although containing much that is merely legendary, an important source of information, not only on the affairs of this monastery, but also on the early history of Germany. The _Codex Hirsaugiensis_ was edited by A. F. Gfrorer and printed at Stuttgart in 1843.