Otto II, Count of Nassau-Siegen
Count Otto II of Nassau-Siegen and his wife Countess Adelaide of Vianden. Design drawing by Bernard van Orley for the tapestry from the series with the genealogy of the House of Nassau, 1530–1535. Metropolitan Museum of Art, New York City.
Count of Nassau-Siegen
Coat of arms
Reign	1343–1350/1351
Predecessor	Henry I
Successor	John I
Full name	Otto II, Count of Nassau-Siegen
Native name	Otto II. Graf von Nassau-Siegen
Born	c. 1305
Died	between 6 December 1350 and 25 January 1351
Noble family	House of Nassau-Siegen
Spouse(s)	Adelaide of Vianden
Issue Detail	John I Henry Otto
Father	Henry I of Nassau-Siegen
Mother	Adelaide of Heinsberg and Blankenberg [nl]

Count Otto II of Nassau-Siegen^{[note 1]} (c. 1305 – between 6 December 1350 and 25 January 1351), German: Otto II. Graf von Nassau-Siegen, was since 1343 Count of Nassau-Siegen^{[note 2]} (a part of the County of Nassau). He descended from the Ottonian Line of the House of Nassau.

Otto is not considered to have been a good regent. His short reign was a succession of feuds during which the country was devastated and the sources of prosperity were blocked.^[1][2]

Otto was born c. 1305^{[3][4][note 3]} as the eldest son of Count Henry I of Nassau-Siegen and Lady Adelaide of Heinsberg and Blankenberg [nl].^[3][4]

In 1336, Otto and his younger brother Henry concluded a provisional division treaty for their father's county. However, Henry's marriage in 1339 led to conflict between the two brothers.^[5] Otto even forged an alliance with Landgrave Herman I of Hesse [de] against Henry in 1340.^[1] A new division treaty followed on 18 June 1341,^[5] which assigned to Otto the Siegerland, the Mark Herborn with Dillenburg and the district of Haiger, as well as Löhnberg.^[1]

Otto succeeded his father in July or August 1343.^[3] The following year, Otto sold castle and lordship of Löhnberg to Count palatine Rupert I and Count Gerlach I of Nassau.^[6] On 20 September of that same year, Otto was granted city privileges for Dillenburg by Holy Roman Emperor Louis the Bavarian.^[7]

Otto is not considered to have been a good regent. His short reign was a succession of feuds during which the country was devastated and the sources of prosperity were blocked. To control his expenses, he was forced to pledge possessions frequently and as a result the development of a powerful activity inwardly as well as outwardly was hampered.^[1][2] He was forced to sell the Nassau half of the city of Siegen to the Electorate of Cologne and lost all parts of the Land Wildenburg that Nassau had acquired to the County of Sayn. And in 1349, he had to pledge the parish of Haiger and half of Ginsburg Castle to the lords of Haiger [de] and the Electorate of Cologne.^[8] Otto played no part in imperial politics, he only was a few times at the imperial court, where he obtained 320 guilders annually for himself from the taxes of the city of Wetzlar in 1347.^[1]

In his last feud, against the brothers Gottfried and Wilderich III von Walderdorff [de], Otto was killed^[2][8][9] in a battle, that, according to charters, must have taken place between 6 December 1350 and 25 January 1351.^{[2][note 4]} As participants on Otto's side in the feud are named the counts Henry I of Nassau-Beilstein (Otto's younger brother),^[2] John [de] and Emicho II of Nassau-Hadamar [de] (Otto's first cousins),^[8][9][10] Gerlach I, Adolf and John of Nassau (Walramian Line), Thierry III of Looz, Walram of Sponheim and Godfrey IV of Arnsberg [de].^[11] Otto was succeeded by his son John I, who stood under regency of his mother until 1362.^{[12][13][14][15]}

• 
  Siegen Castle, 2011.
• 
  Ginsburg Castle. Photo: Frank Behnsen, 2010.

Otto married (marriage contract 23 December 1331^{[16][17][note 5]}) to Countess Adelaide of Vianden (d. 30 September 1376^{[16][17][note 6]}), daughter of Count Philip II of Vianden^[16] and Countess Adelaide of Arnsberg.^{[18][note 7]}

Otto and Adelaide were related. Otto's great-grandmother, Countess Matilda of Guelders and Zutphen, was a younger sister of Count Gerard III of Guelders and Zutphen, a great-great-grandfather of Adelaide.^[19]

From the marriage of Otto and Adelaide the following children were born:^[16][20]

1. Count John I (c. 1339 – Herborn Castle, 4 September 1416), succeeded his father as Count of Nassau-Siegen. He married on 30 November 1357 to Countess Margaret of the Mark [nl]^{[note 8]} (d. 29 September 1409).
2. Henry the Swashbuckler (d. Kassel, 5 September 1402), was canon at the Cologne Cathedral since 1356.
3. Otto (d. 1384), was canon and provost of Saint Maurice Church in Mainz since 1357 and canon of the Cologne Cathedral and the Mainz Cathedral since 1380.

Otto and Adelaide signed a marriage contract with Count Adolf II of the Mark and Countess Margaret of Cleves, for a son of Nassau to marry a daughter of the Mark,^[17][21] on 14 August 1343.^[17]

The second son, Henry the Swashbuckler, although being a clergyman, was nevertheless a brutal fighter of his time, as the disconcerting epithet that his comrades gave him reveals. He even sometimes attacked his eldest brother John.^[22]

• Ausfeld, Eduard (1887). "Otto II. (Graf von Nassau)". Allgemeine Deutsche Biographie (in German). Vol. Band 24. Leipzig: Duncker & Humblot. pp. 707–708.
• Becker, E. (1983) [1950]. Schloss und Stadt Dillenburg. Ein Gang durch ihre Geschichte in Mittelalter und Neuzeit. Zur Gedenkfeier aus Anlaß der Verleihung der Stadtrechte am 20. September 1344 herausgegeben (in German) (Neuauflage ed.). Dillenburg: Der Magistrat der Stadt Dillenburg.
• Dek, A.W.E. (1970). Genealogie van het Vorstenhuis Nassau (in Dutch). Zaltbommel: Europese Bibliotheek.
• Huberty, Michel; Giraud, Alain & Magdelaine, F. & B. (1981). l'Allemagne Dynastique (in French). Vol. Tome III: Brunswick-Nassau-Schwarzbourg. Le Perreux: Alain Giraud. ISBN 2-901138-03-9.
• Lück, Alfred (1981) [1967]. Siegerland und Nederland (in German) (2nd ed.). Siegen: Siegerländer Heimatverein e.V.
• De Roo van Alderwerelt, J.K.H. (1960). "De graven van Vianden. Bijdrage tot een genealogie van het geslacht der graven van Vianden tot de vererving van het graafschap in het Nassause huis". De Nederlandsche Leeuw, Maandblad van het Koninklijk Nederlandsch Genootschap voor Geslacht- en Wapenkunde (in Dutch). 1960 (6): 196.
• von Stramberg, Chr. (1865). Denkwürdiger und nützlicher Rheinischer Antiquarius, welcher die wichtigsten und angenehmsten geographischen historischen und politischen Merkwürdigkeiten des ganzen Rheinstroms, von seinem Ausflusse in das Meer bis zu seinem Ursprunge darstellt. Von einem Nachforscher in historischen Dingen. Mittelrhein. Der II. Abtheilung. 13. Band. Der Rheingau. Historisch und topografisch (in German). Vol. Vierter Band. Coblenz: Rud. Friedr. Hergt.
• Vorsterman van Oyen, A.A. (1882). Het vorstenhuis Oranje-Nassau. Van de vroegste tijden tot heden (in Dutch). Leiden & Utrecht: A.W. Sijthoff & J.L. Beijers.

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