The Battle of Rheinfelden was a military event in the course of the Thirty Years' War, consisting in fact of two battles fought in 1638 to the north and south of the present-day town of Rheinfelden, between a mercenary army led by Bernhard of Saxe-Weimar and an Holy Roman Empire army led by Johann von Werth. Bernhard was defeated in the first battle but managed to defeat and capture Von Werth in the second.