NASSAU, now forming the bulk of the government district of Wiesbaden, in the Prussian province of Hesse-Nassau, was till 1866 an independent and sovereign duchy of Germany, consisting of a compact mass of territory, 1830 square miles in area, bounded on the S. and W. by the•Main and Rhine, on the N. by Westphalia, and on the E. by Hesse. This territory is divided into two nearly equal parts by the river Lahn, which flows from east to west into the Rhine. The southern half is almost entirely occupied by the Taunus Mountains, which attain a height of 2900 feet in the Great Feldberg, while to the north of the Lahn is the barren Westerwald, culminating in the Salzburgerkopf (2000 feet). The valleys and low-lying districts, especially the Rheingau, are very fertile, producing abundance of grain, flax, hemp, and fruit ; but by far the most valuable product of the soil is its wine, which includes several of the choicest Rhenish varieties (Johannisberger, Marcobrunner, Assmannshauser, &c.). Nassau is one of the most thickly wooded regions in Germany, about 42 per cent. of its surface being occupied by forests, which yield good timber and harbour large quantities of game. The rivers abound in fish, - the salmon fisheries on the Rhine being especially important. There are upwards of a hundred mineral springs in the district, most of which formerly belonged to the duke, and afforded him a considerable part of his revenue. The best-known are those of Wiesbaden, Ems, Soden, Schwalbach, Schlangenbad, Geilnau, and Fachingen. The other mineral wealth of Nassau includes iron, lead, copper, building • unimportant, but a brisk trade is carried on by rail and inhabitants, of whom 242,000 were Protestants (including the reigning house), 215,000 Roman Catholics, and 7000 Jews. The ecclesiastical jurisdiction was in the hands of the Protestant bishop of Wiesbaden and the Roman Catholic bishop of Limburg. Education was amply proguldens (L400,000). It furnished a contingent of 6000 men to the army of the German Confederation.

During the Roman period the district enclosed by the Lahn, the Main, and the Rhine was at first occupied by the Mattiaci and then by the Alemanni. The latter were subdued by the Franks under Clovis in 496, and at the partition of Verdun in 843 the country became part of the Eastern or German empire. Christianity seems to have been introduced in the 4th century. The founder of the house of Nassau is usually recognized in Count Otho of Laurenburg, brother of King Conrad I., who flourished on the banks of the Lahn in the 10th century. Ills successors afterwards took the title of counts of Nassau, from a castle which they erected on a steep hill overlooking the Lahn, and in 1192 transferred their allegiance from the archbishop of Treves to the emperor of Germany. In 1255 Walram and Otho, the two sons of Count Henry the Rich, divided between them their paternal inheritance, which had in the meantime been steadily increasing, and founded the twit) Nassovian dynasties which have flourished down to our own times.

The fortunes of the Othonian or younger branch have been the more brilliant, but belong properly to the history of Holland. In 1564 Count William of Nassau, the hero of the Dutch war of independence, succeeded to the principality of Orange, which furnished the historical title of himself and his descendants. The house is now represented by the king of the Netherlands.

Adolf of Nassau, the son of the founder of the elder or Walram line, and progenitor of the dukes of Nassau, became emperor of Germany in 1292, but was defeated and slain in 1298 by his rival Albert of Austria. In 1366 the head of the house was created a prince of the empire, and the Reformation was introduced in the second half of the 16th century. The territories of the house of Walram were frequently partitioned among various branch lines, few of which perpetuated themselves beyond a few generations. At the beginning of the 19th century we find two lines still flourishing - Nassau-Ufingen and Nassau-Weilburg. Both these joined the Rhenish Confederation in 1806, and the prince of NassauUfingen, as head of his family, received the ducal title from the hands of Napoleon. After the battle of Leipsic both princes threw in their lot with the allies. In 1816 the duke of Nassau-Ufingen died, and the prince of Weilburg succeeded to the whole of the Nassovian territory, with the title of duke of Nassau.

This prince had already, in 1814, granted his subjects a limited constitution, providingfor two representative chambers on a landed-property basis, and this came into force in 1818. The estates, however, came almost at once into collision with the duke on the question of the ducal domains, and the dissensions arising from this source were not compromised till 1834. In 1835 the duchy took an important step in the development of its material prosperity by joining the Zollverein. In 1848 Duke Adolf was compelled to yield to the temper of the times and grant a more liberal constitution, with a single chamber elected by universal suffrage ; but the following years witnessed a series of reactionary measures which reduced matters to their former unsatisfactory condition.' The duke adhered steadfastly to his Conservative principles, while his people showed their sympathies by returning one Liberal chamber after another. In 1866, though the chambers refused a vote of credit for military purposes, the duke espoused the cause of Austria, and in doing so sealed the fate of his duchy. A little later he was a fugitive before the Prussian troops, and on October 3d, 1866, Nassau was formally incorporated with the kingdom of Prussia.

The little town of Nassau, on the right bank of the Lahn, 15 miles above Coblenz, is interesting as the birthplace of the celebrated Prussian statesman, Baron Stein. Adjacent are Burg Stein, his ancestral seat, and Burg Nassau, the cradle of the Nassovian dukes. Nassau is said to have existed as early as the 8th century under the name of Nasonga. Population (1880) 1786.

See Sehliephake, Geschichte von Nassau, 180-75; Arnold', Geschichte von Nassau-Oranien; the Annals of the "Verein ftir Nassauische Alterthumsktinde nod Geschlchtsforsehung-; Daniel, Handlyuch der Geographie, 5th ed., 1881.