NASSAU, a territory of Germany, now forming the bulk of the government district of Wiesbaden, in the Prussian province of Hesse-Nassau, but until 1866 an independent and sovereign duchy of Germany. It consists of a compact mass of territory, 1830 sq. m. 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 ft. in the Great Feldberg, while to the north of the Lahn is the barren Westerwald, culminating in the Salzburgerkopf (2000 ft.). 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, such as Johannisberger, Marcobrunner and Assmannshauser. Nassau is one of the most thickly wooded regions in Germany, about 42% 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 F achingen. The other mineral wealth of Nassau includes iron, lead, copper, building stone, coals, slate, a little silver and a bed of malachite. Its manufactures, including cotton and woollen goods, are unimportant, but a brisk trade is carried on by rail and river in wine, timber, grain and fruit. There are few places of importance besides the above-named spas; Höchst is the only manufacturing town. Wiesbaden, with 100,955 inhabitants, is the capital of the government district as it was of the duchy. In 1864 the duchy contained 468,311 inhabitants, of Whom 242,000 were Protestants, 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 provided for in numerous higher and lower schools. The annual revenue of the dukedom was about £400,000 and it furnished a contingent of 6000 men to the army of the German Confederation.

History.—During the Roman period the district enclosed by the Rhine, the Main and the Lahn was occupied by the Mattiaci and later by the Alamanni. The latter were subdued by the Franks under Clovis at the end of the 5th century, and at the partition of Verdun in 843 the country became part of the East Frankish or German kingdom. Christianity seems to have been introduced in the 4th century. The founder of the house of Nassau is usually regarded as a certain Drutwin (d. 1076), who, with his brother Dudo, count of Laurenburg, built a castle on a hill overlooking the Lahn, near the present town of Nassau. Drutwin's descendant Walram (d. 1198) took the title of count of Nassau, and placed his lands under the immediate suzerainty of the German king; previously he had been a vassal of the archbishop of Trier. Then in 1255 Walram's grandsons, Walram and Otto, divided between them their paternal inheritance, which had been steadily increasing in size. Walram took the part of Nassau lying on the left bank of the Lahn and made Wiesbaden his residence; Otto took the part on the right bank of the river and his capital was Siegen. The brothers thus founded the two branches of the house of Nassau, which have flourished to the present time.

The fortunes of the Ottonian, or younger line, belong mainly to the history of the Netherlands. The family was soon divided into several branches, and in the 15th century one of its members. Count Engelbert I. (d. 1442), obtained through marriage lands in Holland. Of his two sons one took the Dutch, and the other the German possessions of the house, but these were united again in 1504 under the sway of John, count of Nassau-Dillenburg, the head of a branch of the family which, in consequence of a series of deaths, the last of which took place in 1561, was a few years later the sole representative of the descendants of Count Otto. John’s son was Count William the Rich (d. 1559), and his grandson was the hero, William the Silent, who inherited the principality of Orange in 1544 and surrendered his prospective inheritance in Nassau to his brother John (d. 1606). William and his descendants were called princes of Orange-Nassau, and the line became extinct when the English king William III. died in 1702. Meanwhile the descendants of Count John, the rulers of Nassau, were flourishing. They were divided into several branches, and in 1702 the head of one of these, John William Friso of Nassau-Dietz (d. 1711), whose ancestor had been made a prince of the Empire in 1654, inherited the title of prince of Orange and the lands of the English king in the Netherlands. A few years later in 1743 a number of deaths left John William’s son, William, the sole representative of his family, and as such he ruled over the ancestral lands both in Nassau and in the Netherlands. In 1806, however, these were taken from a succeeding prince, William VI., because he refused to join the Confederation of the Rhine. Some of them were given in 1815 to the other main line of the family, the one descended from Count Walram (see below). In 1815 William VI. became king of the Netherlands as William I., and was compensated for this loss by the grant of parts of Luxemburg and the title of grand duke. When in 1890 William’s male line died out Luxemburg, like Nassau, passed to the descendants of Count Walram. In the female line he is now represented by the queen of the Netherlands.

Adolph of Nassau, a son of Walram, the founder of the elder line 'of the house of Nassau, became German king in 1292, but was defeated and slain by his rival, Albert of Austria, in 1298. The territories of his descendants were partitioned several times, but these branch lines did not usually perpetuate themselves beyond a few generations, and Walram’s share of Nassau was again united in 1605 under Louis II. of Nassau-Weilburg (d. 1626). Soon, however, the family was again divided; three branches were formed, those of Saarbrücken, Idstein and Weilburg, the heads of the first two becoming princes of the Empire in 1688. Other partitions followed, but at the opening of the 10th century only two lines were flourishing, those of Nassau-Usingen and Nassau-Weilburg. In 1801 Charles William, prince of Nassau-Usingen, was deprived by France of his lands on the left bank of the Rhine, but both he and Frederick William of Nassau-Weilburg, who suffered a similar loss, received ample compensation. In 1806 both Frederick William and Frederick Augustus, the brother and successor of Charles William, joined the Confederation of the Rhine and received from Napoleon the title of duke, but after the battle of Leipzig they threw in their lot with the allies, and in 1815 joined the German Confederation. As a result of the changes of 1815 Frederick Augustus of Nassau-Usingen ceded some of his newly-acquired lands to Prussia, receiving in return the greater part of the German possessions of the Ottonian branch of the house of Nassau (see above). In March 1816 he died without sons and the whole of Nassau was united under the rule of Frederick William of Nassau-Weilburg as duke of Nassau. Already in 1814 Frederick William had granted a constitution to his subjects, which provided for two representative chambers, and under his son William, who succeeded in 1816, the first landtag met in 1818. At once, however, it came into collision with the duke about the ducal domains, and these dissensions were not settled until 1836. In this year the duchy took an important step in the development of its material prosperity by joining the German Zollverein. In 1848 Duke Adolph, the son and successor of Duke William, was compelled to yield to the temper of the times and to grant a more liberal constitution to Nassau, but in the following years a series of reactionary measures reduced matters to their former unsatisfactory condition. The duke adhered steadfastly to his conservative principles, While his people showed their sympathies by electing one liberal landtag after another. In 1866 Adolph espoused the cause of Austria, sent his troops into the field and asked the landtag for money. This was refused, Adolph was soon a fugitive before the Prussian troops, and on the 3rd of October 1866 Nassau was formally incorporated with the kingdom of Prussia. The deposed duke entered in 1867 into a convention with Prussia by which he retained a few castles and received an indemnity of about £1,500,000 for renouncing his claim to Nassau. In 1890, on the extinction of the collateral line of his house, he became grand-duke of Luxemburg, and he died on the 17th of November 1905.

The town of Nassau (Lat. Nasonga) on the right bank of the Lahn, 15 m. above Coblenz, is interesting as the birthplace of the Prussian statesman, Freiherr von Stein. Pop. (1905) 2238. It has a Roman Catholic and an Evangelical church, while its main industries are brewing and mining. Near the town are the ruins of the castle of Stein, first mentioned in 1138, with a marble statue of Stein, while the ruins of the ancestral castle of the house of Nassau may also be seen.

For the history of Nassau see Hermes, Geschichte der Grafen von Nassau bis 1255 (Cologne, 1843); von Schütz, Geschichte des Herzogtums Nassau (Wiesbaden, 1853); von Witzleben, Genealogie und Geschichte der Fürstenhauses Nassau (Stuttgart, 1855); F. W. T. Schliephake and K. Menzel, Geschichte von Nassau (Wiesbaden, 1865–1889); the Codex diplomatlcus nassoicus, edited by K. Menzel and W. Sauer (1885–1887); and the Armalen des Vereins für nassauische Altertumskunde und Geschichtsforschung (1827 fol.).