Robert I, Count of Nassau

Robert I of Nassau (German: Ruprecht; c. 1090 – c. 1154) was from 1123 co-Count of Laurenburg and would later title himself the first Count of Nassau. The House of Nassau would become an important aristocratic family in Germany, from which are descended through females the present-day royals of the Netherlands and Luxembourg, while officially belonging to this House.

Robert was the eldest son of Count Dudo-Henry of Laurenburg (German: Dudo-Heinrich von Laurenburg) and Anastasia of Arnstein an der Lahn (near present-day Obernhof), daughter of Count Louis II of Arnstein. Count Dudo, considered the founder of the House of Nassau, had built the castle of Laurenburg around 1080. He had also laid the foundations of Nassau Castle in present-day Nassau, Germany, around 1100, on land belonging to the Bishopric of Worms. After 1120, Robert, ruled from Nassau Castle together with his brother Arnold I.

In 1124, Robert became the Bishopric of Worms's Vogt over the Weilburg Diocese. He inherited this position from the Hessian Count Werner IV, Count of Gröningen. Idstein, which had come under the control of Count Dudo in 1122, was also added to this fief. Through this, Robert was able to decisively expand the possessions of the House of Nassau. He gained, among other lands, the village of Dietkirchen and established himself in the Haiger Mark.

Along with numerous property and lordship rights in the Westerwald and Dill River region, Weilburg's territory included the former Königshof Nassau, which had fallen to Weilburg in 914. This did not, however, settle the dispute with the Bishop of Worms over the legality of constructing Nassau Castle. When Robert I began calling himself the Count of Nassau after the castle, the Worms Bishopric disputed the title. The title was only confirmed through the intervention of the Archbishop of Trier in 1159, about five years after Robert’s death, under his son Walram I.

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