in 1547, the Treaty of Erfurt in 1572, when the city became part of Saxe-Coburg, and the Thirty Years' War resulted in Gotha's decline. The local castle, Grimmenstein, was razed by Imperial troops in 1572.

The turnaround was brought about by the selection of Gotha as a ducal residence in the 1640 territorial partition, when Ernest the Pious founded the duchy