Saxe-Gotha-Altenburg

Saxe-Gotha-Altenburg () was a duchy ruled by the Ernestine branch of the House of Wettin in today's Thuringia, Germany. The extinction of the line in 1825 led to a major re-organisation of the Thuringian states.

==History== thumb|left|Friedenstein Castle, Gotha In 1640 the sons of the late Ernestine duke John II of Saxe-Weimar divided their paternal heritage (Ernestinische Teilung) whereby Duke Ernest the Pious, a younger son, received the newly established Duchy of Saxe-Gotha. In 1636 Ernest had married Elisabeth Sophie, the only child of Duke John Philip of Saxe-Altenburg. Upon her father's death in 1639, the Duchy of Saxe-Altenburg passed to her uncle Duke Frederick William II and her cousin Frederick William III.