Battle of Rheinfelden 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 . Prelude . Following the Swedish defeat at the Battle of Nördlingen in 1634 , Bernhard ' s mercenary army had come under the pay of France . Having been pushed back over the Rhine by the Imperial advance Bernhard ' s army had settled in Alsace during 1635 and had done little except help repulse the Imperial invasion of France under the Cardinal - Infante Ferdinand and General Matthias Gallas in 1636 . Early in February 1638 , having been prodded by the French government Bernhard advanced his army to the Rhine in order to find a crossing . Arriving at an important crossing point at the town of Rheinfelden , Bernhard prepared to invest the town from the south and using the ferry at Beuggen threw troops across the river in order to complete the investment from the north . The attack on the town was to be made on March 1 . In order to prevent this , the Imperialists , under the Italian mercenary Count Federico Savelli and Johann von Werth , moved through the Black Forest to attack Bernhard ' s army and relieve the town . The First Battle . The advance guard of the Imperial army , having advanced down the right bank of the river , was pushed back by Bernhard . This gave him time to deploy more troops and artillery onto the north bank of the river . However , by the time Savelli appeared with the main body of his force only half of Bernhard ' s army had made it to the north bank . Bernhard drew up his army to prevent Savelli from relieving the town . Savelli deployed the Imperial army opposite Bernhard but because of the rough ground there was little chance for both armies to retain their formation . Savelli drove back Berhard ' s left flank while on the opposite end of the field Bernhard routed the Imperial right . Like a revolving door both armies swung round giving Savelli the chance to capture the ferry and cut off Bernhard from his troops on the south back . At the days end the armies were facing each other in the positions that the other had started the battle in . Bernhard ' s March . Although the Imperialists held the field Bernhard ' s losses were not serious and he resolved to unite both parts of his army . Avoiding Imperialist detachments Bernhard marched east along the Rhine to the village of Laufenburg . There , having crossed the Rhine and united his army , Bernhard turned back towards Rheinfelden . The Second Battle . Believing Bernhard ' s army defeated and scattered , the Imperialist army failed to take precautions . Around 7 am Savelli ' s outposts were astonished to see Bernhard ' s army approaching and withdrew towards Rheinfelden to report Bernhard ' s presence as Savelli and Werth assembled their army in haste . Bernhard had his artillery fire three times into the Imperial ranks before a final charge broke the Imperialist army . Troops coming out of Rheinfelden to help were also caught by Bernhard and forced to surrender . Both Savelli and Werth were captured . Aftermath . Bernhard ' s victory enabled him to march north along the Rhine to initiate the siege of Breisach .