The Wettin Elector John George I of Saxony stipulated in his will dated 20 July 1652 that his three younger sons should receive secundogeniture principalities. After the elector died on 8 October 1656, his sons concluded the "friend-brotherly main treaty" in the Saxon residence of Dresden on 22 April 1657 and a further treaty in 1663 delineating their territories and sovereign rights definitively. The treaties created three duchies: Saxe-Zeitz, Saxe-Weissenfels, and Saxe-Merseburg.
The area of Saxe-Merseburg stretched to the western city limits of Leipzig. The customs station was in what is now the inner city district of Lindenau.
After the death of the last male heir of the Saxon branch line in 1738, the Duchy of Saxe-Merseburg fell back to the Electorate of Saxony.
1694-1731 Maurice Wilhelm (born: 5 February 1688 in Merseburg; died: 21 April 1731 in Merseburg), until 1712 under the regency of Elector Frederick August I of Saxony and the guardianship of his mother Erdmuthe Dorothea of Saxe-Zeitz
1731-1738 Heinrich (born: 2 September 1661 in Merseburg; died: 28 July 1738 in Doberlug), previously already Duke of Saxe-Merseburg-Spremberg
Cadet lines
To supply his three younger sons with incomes befitting a duke, Duke Christian I created apanages for his younger sons during his lifetime. These territories remained dependent on the main line and their sovereignty was severely restricted. They were named after their owner's residences and disappeared with the death of their first duke, because none of them fathered surviving male heirs. Before it died out, the Saxe-Merseburg-Spremberg line inherited all of Saxe-Merseburg.
Until 1715 August (born: 15 February 1655 in Merseburg; died: 27 March 1715 in Zörbig), Duke of Saxe-Merseburg-Zörbig
Until 1690 Philipp (born: 26 October 1657 in Merseburg; died: 1 July 1690 in Fleurus), Duke of Saxe-Merseburg-Lauchstädt
Until 1731 Heinrich (born: 2 September 1661 in Merseburg; died: 28 July 1738 in Doberlug), Duke of Saxe-Merseburg-Spremberg until 1731, inherited Saxe-Merseburg in 1731
References
Martina Schattkowsky/Manfred Wilde (Hg.): Sachsen und seine Sekundogenituren. Die Nebenlinien Weißenfels, Merseburg und Zeitz (1657–1746). Schriften zur Sächsischen Geschichte und Volkskunde, Band 33. Leipziger Universitätsverlag, Leipzig 2010, ISBN978-3-86583-432-4.
Manfred Wilde: Das Barockschloss Delitzsch als Witwensitz der Herzöge von Sachsen-Merseburg. In: Barocke Fürstenresidenzen an Saale, Unstrut und Elster, edited by the Museumsverbund Die fünf Ungleichen, Michael Imhof Verlag, Petersberg 2007, pp. 264–276, ISBN978-3-86568-218-5.
