The last decade of his life was made cheerful by his marriage with Ernestine Muller, who shared all his interests and learned Greek to help him with collations.
Also an early possession of the Wettins, Gotha fell at the partition of 1485 to the Albertine branch of the family, but was transferred to the Ernestine branch by the capitulation of Wittenberg of 1547.
This deed transferred the electoral title and a large part of the electoral lands from the Ernestine to the Albertine branch of the house, whose astute representative, Maurice, had taken the imperial side during the war.
The political history of the parts of Saxony left by the capitulation of Wittenberg to the Ernestine line, which occupy the region now generally styled Thuringia (Thuringen), is mainly a recital of partitions, reunions, redivisions and fresh combinations of territory among the various sons of the successive dukes.
Then suddenly invading the Ernestine lands while the elector John Frederick was campaigning against the imperialists on the Danube, he forced that prince to return hastily to Saxony, and thus weakened the forces opposed to the emperor.
Only a few scattered territories were reserved for John Frederick's sons, although these were increased by the treaty of Naumburg in 1554, and on them were founded the Ernestine duchies of Saxe-Gotha, Saxe-Weimar, Saxe-Coburg, Saxe-Meiningen and Saxe-Altenburg.