Ernst von Mansfeld Ernst , Graf von Mansfeld ( c . 1580 – 29 November 1626 ) , was a German military commander during the early years of the Thirty Years ' War . Biography . Mansfeld was an illegitimate son of Graf Peter Ernst von Mansfeld , and passed his early years in his father ' s palace at Luxembourg . He gained his earliest military experiences in Hungary , where his half - brother Charles ( 1543 – 1595 ) , also a soldier of renown , held a high command in the imperial army . Later he served under the Archduke Leopold , until that prince ' s ingratitude , real or fancied , drove him into the arms of the enemies of the house of Habsburg . Although remaining a Roman Catholic he allied himself with the Protestant princes , and during the earlier part of the Thirty Years ' War he was one of their foremost champions . He was despatched by Charles Emmanuel , duke of Savoy , at the head of about 2000 men to aid the revolting Bohemians when war broke out in 1618 . He took Pilsen , but in the summer of 1619 he was defeated at the Battle of Sablat ; after this he offered his services to the emperor Ferdinand II and remained inactive while the titular king of Bohemia , Frederick V , elector palatine of the Rhine , was driven in headlong rout from Prague . Mansfeld , however , was soon appointed by Frederick to command his army in Bohemia , and in 1621 he took up his position in the Upper Palatinate , successfully resisting the efforts made by Tilly to dislodge him . From the Upper he passed into the Rhenish Palatinate . Here he relieved Frankenthal and took Hagenau ; then , joined by his master , the elector Frederick , he defeated Tilly at Wiesloch ( 25 April 1622 ) and plundered Alsace and Hesse . But Mansfeld ' s ravages were not confined to the lands of his enemies ; they were ruinous to the districts he was commissioned to defend . At length Frederick was obliged to dismiss Mansfeld ' s troops from his service . Then joining Christian of Brunswick the count led his army through Lorraine , devastating the country as he went , and in August 1622 was defeated by the Spaniards at Fleurus . He next entered the service of the United Provinces and took up his quarters in East Frisia , capturing fortresses and inflicting great hardships upon the inhabitants . A mercenary and a leader of mercenaries , Mansfeld often interrupted his campaigns by journeys made for the purpose of raising money , or in other words of selling his services to the highest bidder , and in these diplomatic matters he showed considerable skill . About 1624 he paid three visits to London , where he was hailed as a hero by the populace , and at least one to Paris . James I , being the father - in - law of Frederick V , Elector Palatine , was anxious to furnish him with men and money for the recovery of the Palatinate , but it was not until January 1625 that Mansfeld and his army of " raw and poor rascals " sailed from Dover to the Netherlands . Later in the year , the Thirty Years ' War having been renewed under the leadership of Christian IV of Denmark , he re - entered Germany to take part therein . But on 25 April 1626 Wallenstein inflicted a severe defeat upon him at the bridge of Dessau . Mansfeld , however , quickly raised another army , with which he intended to attack the hereditary lands of the house of Austria , and pursued by Wallenstein he pressed forward towards Hungary , where he hoped to accomplish his purpose by the aid of Bethlem Gabor , prince of Transylvania . But when Gabor changed his policy and made peace with the emperor , Mansfeld was compelled to disband his troops . He set out for Venice , but when he reached Rakowitza near Sarajevo , in Bosnia , he was taken ill , and here he died on 29 November 1626 . He was buried at Split .