thumb|right|200px|[[Bust (sculpture)|Bust of Mercy on display in the Ruhmeshalle in Munich.]]
Franz Freiherr von Mercy (or Merci), Lord of Mandre and Collenburg ( 1597 – 3 August 1645), was a German field marshal in the Thirty Years' War who fought with distinction for the Imperial side and was commander-in-chief of the Bavarian army from 1643 to 1645. In that role, he destroyed a French army at Tuttlingen (1643), stalemated another at Freiburg (1644), destroyed a third French army at Herbsthausen (1645) and was killed at the Second Battle of Nördlingen (1645).
Biography
Early life and career
Franz von Mercy was born at Longwy around 1597. His parents were Pierre Ernest de Mercy († 1619), governor of Longwy and Chamberlain of Duke Charles III of Lorraine, and Anne du Hautoy. Of his many siblings, his brothers Heinrich (1596–1659) and Kaspar (1600–1644) also became generals in the Imperial or Bavarian army. Franz entered military service most likely in the army of the Catholic League around the beginning of the Thirty Years' War and changed over to imperial service later on. In 1625 he held the rank of captain in the regiment of Hannibal von Schauenburg and in 1626 he was mentioned as chamberlain of Archduke Leopold V of Tyrol.
By 1630 he had attained the rank of Obristwachtmeister, and after distinguishing himself at the first Battle of Breitenfeld, where the Imperial army was destroyed and Mercy wounded, he commanded a regiment of foot with the rank of Obrist on the Rhine. He repelled a Swedish attack led by Gustaf Horn on Konstanz in 1633. For his brother Ludwig (born 1614), who died of his injuries at the age of 19 on 6 October 1633 shortly after the last attack by the Swedes, Franz von Mercy had an artistic bronze epitaph made in the Konstanz Minster, which is still preserved today.
He became a general with the rank of General-Feldwachtmeister, and in 1635, 1636 and 1637 took part in further campaigns under command of Duke Charles IV of Lorraine on the Rhine and Doubs.
Bavarian general
In September 1638, the elector of Bavaria made him Generalfeldzeugmeister in the army of Bavaria, then the second largest army in Germany. The following year, Mercy took part at the campaign of the main Imperial army under Archduke Leopold Wilhelm and Ottavio Piccolomini against the Swedes under Johan Banér. Mercy helped prevent the Swedes from invading Franconia. Repelling the Swedes and their allies to Hesse-Kassel, the Imperials and Bavarians laid in camp near Fritzlar for weeks in the immediate vicinity of their opponents. As both sides avoided a major battle, the Archduke concluded his campaign with capturing Höxter at the Weser river in October. Mercy himself returned to south-west Germany in late autumn.
thumb|Painting of the siege of Neunburg in 1641 by [[Pieter Snayers]]
Mercy protected the Imperial Diet in Regensburg with his troops from a Swedish attack by Banér in January 1641. When the thawing of the icy Danube stopped the Swedish advance, Imperial and Bavarian troops rallied and forced the Swedes to retreat in flight. In pursuit of the Swedes into Bohemia, the vanguard under Mercy's brother Kaspar repulsed the Swedish rearguard under Erik Slang into Neunburg vorm Wald, where they capitulated to the Imperial-Bavarian army under Piccolomini and Franz von Mercy after several days resistance. Banér escaped just ahead of Mercy and Piccolomini over the Preßnitz Pass into Saxony. Continuing on the heels of the Swedes, Mercy had to hand over command to his superior Joachim Christian von Wahl at Zeitz on 1 May. Without Banér, who died en route, the Swedes joined the Lüneburg army sieging Wolfenbüttel. In an attempt to relieve the fortress, Mercy ambushed and captured 500 besiegers on 28 June. The next day, he commanded the left wing in battle against the siege army, who could not driven from their positions. Only after Imperial and Bavarian forces had captured numerous towns in the surrounding countryside, their opponents abandoned the siege of Wolfenbüttel in September. Until winter, Mercy took part in the capture of Einbeck and a futile siege of Göttingen in November.
In 1642 he received the command of the Bavarian troops in Swabia. In the course of the year he drove the opposing troops from Swabia and parts of the Breisgau. He was appointed a member of the Fruitbearing Society by Louis I, Prince of Anhalt-Köthen. Mercy was now considered one of the foremost soldiers in Europe, and was made Generalfeldmarschall on 31 May 1643.