Nassau until the recent re-establishment of the German Empire an independent duchy of Germany, but now constituting the southwestern part of the Prussian province of Hesse-Nassau, is situated between 49° 50' and 500 50' N. lat., and 70 30' and 8° 45' E long. It is bounded on the west and south by the Main and the Rhine, the Prussian-Rhenish provinces, and the former grand-duchy of Hesse; on the east by the extinct Hesse and Frankfort territories; and on the north by the province of Westphalia. It covers an area of 1808 square miles, with a population of 468,311 in 1866. The country possesses very great physical advantages. In its southern districts, nearly the whole of its area is occupied by the Taunus Mountains, whose highest point, the Great Feldberg, attains an elevation of about 2750 feet. This range includes within its boundaries the fertile valleys known as the Rheingau. The northern part of the duchy includes the barren highlands of the Westerwald, whose most considerable peak, the Salzburger Head, is nearly 2000 feet high. Besides the Rhine and the Main, which are the boundary rivers, Nassau is traversed from east to west by the Lahn, which becomes navigable at Weilburg, and is augmented by the confluence of numerous other streams, as the Weil, Ems, Aar, Dill, Elbe. The productiveness of the soil is proved by the excellent quality of the numerous vegetable products, which include corn, hemp, flax, tobacco, vegetables, and fruits, especially grapes, which yield some of the best of Rhenish wines. In the more mountainous districts, iron, lead, copper, and some silver are obtained, also much good building-stone, marble, and coal; the chief mineral wealth is, however, derived from the numerous springs, which, directly and indirectly, bring the province a clear annual gain of nearly 100,000 dollars. The most noted of these springs, of which there are more than one hundred, are Wiesbaden, Weilbach, Langen-Schwalbach, Schlangenbad, Ems, Fachingen, Selters, Soden, and Geilnau.
In tracing the history of Nassau to its earliest origin, we find that the districts now known by that name were anciently occupied by the Allemanni, and on the subjugation of the latter people by the Franks became incorporated first with the Frankish, and next with the German Empire. Among the various chiefs who raised themselves to independent power in this portion of the Frankish territories, one of the most influential was Otto of Laurenburg, brother of king Conrad I, who became the founder of two distinct lines of princes. The heads of these lines were Walram and Otto, the sons of count Henry I, who, in 1255, divided the land between them. Walram II, the eldtr, was the progenitor of the house of Laurenburg, which, towards the close of the 12th century, assumed its present name of Nassau from the name of its chief stronghold; while Otto, the younger, by his marriage with the heiress of Gelders, founded the line of Nassau-Gelders, whose last male representative died in 1423, but which still survives through a female branch in the family now occupying the throne of the Netherlands. This junior branch of the house of Nassau, by inheritance from a collateral representative, acquired possession, in 1544, of the principality of Orange; and since that period the representatives of the Otto line have been known as princes of Orange (q.v.). The Walram line, which in 1292 gave an emperor to Germany in the person of Adolf of Nassau, was subdivided by the descendants of that prince into several branches, until, by the successive extinction of the other lines, the Nassau- Weilburg family, which last reigned over the duchy, was left, in 1816, the sole heir and representative of the Walram dynasty in Germany. Nassau was declared a duchy in 1806, and in 1817 duke William granted a new constitution; but during the first sittings of the assembly dissensions arose between the ducal government and the people's representatives, which resulted in an estrangement of ruler and ruled, and were not quieted until 1834. In 1836 Nassau joined the German Zollverein, and its material prosperity thereafter rapidly developed. In 1839 the last duke of Nassau came to the throne in the person of Adolphus William. He experienced the revolutionary days of 1848, but remained in possession of his territory until 1866, when Prussia deposed him because of his alliance with Austria. He is now a pensioner of the Prussian government.
Christianity was introduced among the people of Nassau at a very early date, probably during the period of Rcme's world rule, after its emperors had become Christians. The presbyter Lubertius, who flourished in the 4th century, preached in these domains; but no stronghold was made here for Christianity until the days of Boniface in the 8th century, about 739. In the 10th and 11th centuries many churches were built and Christianity was fortified by schools. The people, however, were but poorly educated, and at the dawn of the Reformation this country was far behind other German territories. About 1530 Nassau declared for the new faith, and in 1534 joined the Smalcald league. At first decided Lutherans, the Nassau Protestants gradually turned over to the views of the Reformed Church, and in 1582 the theologians of Nassau, protesting against the monster Ubiquity in the Form of Concord, were induced to adopt the Heidelberg Catechism, and in consequence of its relation to the house of Orange, Nassau was brought to accept the ecclesiastical system which prevailed in the Netherlands. (See Staubing, Kirchenu. Ref.-Gesch. Oranien-Nass. Lande [Hadam, 1804]; Hase, Ch. Hist. page 413.) In 1817 the Protestants of Nassau constituted an Evangelical United Church, and a theological seminary is supported at Herborn, where all who look towards the ministry are obliged to spend one year after finishing a university curriculum. Nearly half the population of Nassau belong to the Romamn Catholic Church, which is under the ecclesiastical jurisdiction of the bishop of Limburg, who is assisted by a board of commissioners, located at Eltville, on the Rhine. There are also about 8000 persons who belong to the Jewish and other persuasions. Ample provisions are made in the territory for popular education, in furtherance of which there are upwards of 700 elementary schools, with about 1000 teachers, 10 normal schools, a gymnasium, various training, polytechnic, military, and other educational institutions. See Vogel, Beschreib. d. Herzogth. Nassau (Wiesb. 1843-44); Schliephake, Gesch. v. Nassau (ib. 1864-70, 3 volumes, 8vo).