The Battle of Freiburg, fought over three days on 3, 5, and 9 August 1644, took place during the Thirty Years' War, near Freiburg im Breisgau, now in Baden-Württemberg. A French army of 16,000, led jointly by Condé and Turenne, sought to relieve the town, which had recently surrendered to a Bavarian force under Franz von Mercy. In what has been described as the bloodiest battle of the war, around half of the French soldiers engaged were killed or wounded, with the Bavarians losing up to a third of theirs. The French claimed victory since Mercy was forced to withdraw, but the result is disputed.
Having captured Freiburg on 28 July, Mercy placed his men in strong defensive positions on the hills outside the town, which the French attacked on 3 and 5 August. Although the assaults made little progress and incurred severe losses, the Bavarians also suffered heavy casualties and were short of supplies. On 9 August, Mercy learned a detachment under Turenne was marching into his rear to cut off his supply lines, and ordered a general retreat, leaving a garrison in Freiburg. Apart from a brief skirmish with Turenne's cavalry next day, they withdrew in good order, despite abandoning their baggage train and several guns.
Nevertheless, Freiburg convinced Maximilian I, Elector of Bavaria, that the war could not be won and he began negotiating peace terms. Mercy was ordered to suspend offensive operations, ceding France the strategic initiative, and allowing Condé and Turenne to take control of most of the northern Upper Rhine.