Charles X Gustav of Sweden Charles X Gustav also Carl Gustav , ( 8 November 1622 – 13 February 1660 ) was King of Sweden from 1654 until his death . He was the son of John Casimir , Count Palatine of Zweibrücken - Kleeburg and Catherine of Sweden . After his father ' s death he also succeeded him as Pfalzgraf . He was married to Hedwig Eleonora of Holstein - Gottorp , who bore his son and successor , Charles XI . Charles X Gustav was the second Wittelsbach king of Sweden after the childless king Christopher of Bavaria ( 1441 – 1448 ) and he was the first king of the Swedish " Caroline era " , which had its peak during the end of the reign of his son , Charles XI . He led Sweden during the Second Northern War , enlarging the Swedish Empire . By his predecessor Christina , he was considered " de facto " Duke of Eyland ( Öland ) before ascending to the Swedish throne . His numbering as " Charles X " derives from a 16th - century invention . The Swedish king Charles IX ( 1604 – 1611 ) chose his numeral after studying a fictitious history of Sweden . This king was the fourth actual King Charles , but has never been called " Charles IV " . Heir to the throne . In his early childhood raised in the Swedish court alongside Queen Christina he received an excellent civil education . Later Charles X learned the art of war under Lennart Torstenson , being present at the second Battle of Breitenfeld ( 1642 ) and at Jankowitz ( 1645 ) . From 1646 to 1648 he frequented the Swedish court , supposedly as a prospective husband of his cousin the queen regnant , Christina of Sweden ( 1626 – 89 , reigned 1632 – 54 ) , but her insurmountable objection to wedlock put an end to these anticipations , and to compensate her cousin for a broken half - promise she declared him her successor in 1649 , despite the opposition of the Privy Council headed by Axel Oxenstierna . In 1648 he gained the appointment of commander of the Swedish forces in Germany . The conclusion of the treaties of Westphalia in October 1648 prevented him from winning the military laurels he is said to have desired , but as the Swedish plenipotentiary at the executive congress of Nuremberg , he had an opportunity to learn diplomacy , a science he is described as having quickly mastered . As the recognized heir to the throne , his position on his return to Sweden was dangerous because of the growing discontent with the queen . He therefore withdrew to the isle of Öland until the abdication of Christina on 5 June 1654 called him to the throne . Early days as King . The beginning of Charles X ' s reign concentrated on the healing of domestic discords and on the rallying of all the forces of the nation round his standard for a new policy of conquest . He contracted a political marriage on 24 October 1654 with Hedwig Eleonora , the daughter of Frederick III , Duke of Holstein - Gottorp , by way of securing a future ally against Denmark . The Riksdag which assembled at Stockholm in March 1655 , duly considered the two great pressing national questions : war , and the restitution of the alienated crown lands . Over three days a secret committee presided over by the King decided the war question : Charles X easily persuaded the delegates that a war against Poland appeared necessary and might prove very advantageous ; but the consideration of the question of the subsidies due to the crown for military purposes was postponed to the following Riksdag . In 1659 he proclaimed severe punishment for anyone hunting in the royal game reserve in Ottenby , Öland , Sweden , where he had built a long dry - stone wall separating the southern tip of the island . Second Northern War ( 1655 – 1660 ) . War in Poland - Lithuania . On 10 July 1655 , Charles X left Sweden to engage in a war against the Polish - Lithuanian Commonwealth , in what became the Second ( or Little ) Northern War ( 1655 – 1660 ) . By the time war was declared he had at his disposal 50 , 000 men and 50 warships . Hostilities had already begun with the occupation of Dünaburg in Polish Livonia by the Swedes on 1 July 1655 . Then on 21 July 1655 Swedish army under Arvid Wittenberg crossed into Poland and proceeded towards the encampment of the Greater Poland Levy of the Nobility ( pospolite ruszenie ) encamped among the banks of the Noteć river , with some regular infantry for support . On 25 July the Polish noble levy army capitulated , and the voivodeship s of Poznań and Kalisz placed themselves under the protection of the Swedish King . Thereupon the Swedes entered Warsaw without opposition and occupied the whole of Greater Poland . The Polish king , John II Casimir of Poland ( 1648 – 68 ) of the House of Vasa , eventually fled to Silesia after his armies had suffered defeats . A great number of Polish nobles and their personal armies joined the Swedes , including the majority of the famous Winged Hussars . Many Poles saw Charles X Gustav as a strong monarch who could be a more effective leader than John II Casimir . Meanwhile Charles X Gustav pressed on towards Kraków , which the Swedes captured after a two months ' siege . The fall of Kraków followed a capitulation of the Polish Royal armies , but before the end of the year a reaction began in Poland herself . On 18 November 1655 the Swedes invested the fortress - monastery of Częstochowa , but the Poles defended it and after a seventy days ’ siege the Swedish besiegers had to retire with great loss . This success elicited popular enthusiasm in Poland and gave rise to a nationalistic and religious rhetoric concerning the war and Charles X . He was depicted as tactless and his mercenaries barbaric . His refusal to legalize his position by summoning the Polish diet and his negotiations for the partition of the very state he affected to befriend , awoke a nationalistic spirit in the country . In the beginning of 1656 King John II Casimir returned from exile and the reorganised Polish army , increased in numbers . By this time Charles had discovered that he could more readily defeat the Poles than conquer Poland . What is described as his chief object , the conquest of Prussia , remained unaccomplished , and a new Swedish adversary arose in the elector of Brandenburg , Frederick William I , alarmed by the ambition of the Swedish king . Charles forced the elector , albeit at the point of the sword , to become his ally and vassal ( Treaty of Königsberg , 17 January 1656 ) ; but the Polish national rising now imperatively demanded his presence in the south . For weeks he engaged in the pursuit of Polish divisions engaged in guerrilla tactics in the snow - covered plains of Poland , penetrating as far south as Jarosław in Ruthenian Voivodeship ( województwo ruskie ) , by which time he had lost two - thirds of his 15 , 000 men army with no apparent result . In the meantime , the Russians signed a cease - fire with the Polish - Lithuanian Commonwealth ( Treaty of Vilno of 1656 ) and then pursued a campaign in Livonia and laid siege to Riga , the second largest city in the Swedish Realm . Charles ' s retreat from Jarosław to Warsaw almost ended with disaster , for he returned with the fragments of his host , for his army was trapped by he Polish - Lithuanian armies – amidst three converging armies , in a marshy forest region intersected in every direction by well - guarded rivers – is considered one of his most brilliant achievements . But on 21 June 1656 the Poles retook Warsaw , and four days later Charles was obliged to purchase the assistance of Frederick William I , by the treaty of Marienburg ( 23 June 1656 ) . On 28 July - 30 the combined Swedes and Brandenburgers , 18 , 000 strong , after a three days ’ battle , defeated John Casimir ' s army of 40 , 000 at Warsaw , however the Polish - Lithuanian forces promptly withdrew with no large losses and apparent strong will to fight another day , while Swedish host reoccupied the Polish capital again , causing innumerable destruction to the city and its inhabitants . However , this feat of arms did not have the desired result for Charles , and when Frederick William compelled the Swedish king to open negotiations with the Poles , they refused the terms offered , the war resumed , and Charles concluded an offensive and defensive alliance with the elector of Brandenburg ( Treaty of Labiau , 20 November 1656 ) which stipulated that Frederick William and his heirs should henceforth possess the full sovereignty of East Prussia . War on Denmark . Labiau involved an essential modification of Charles ' s Baltic policy ; but the alliance with the elector of Brandenburg had now become indispensable for him on almost any terms . The difficulties of Charles X in Poland are believed to have caused him to receive the tidings of the Danish declaration of war on 1 June 1657 with extreme satisfaction . He had learnt from Torstensson that Denmark was most vulnerable if attacked from the south , and he attacked Denmark with a velocity which paralysed resistance . At the end of June 1657 , at the head of 8 , 000 seasoned veterans , he broke up from " Bromberg " ( Bydgoszcz ) south of Pomerania and reached the borders of Holstein on 18 July . The Danish army dispersed and the Swedes recovered the duchy of Bremen . In the early autumn Charles ' s troops swarmed over Jutland and firmly established themselves in the duchies . But the fortress of Fredriksodde ( Fredericia ) held Charles ' s smaller army at bay from mid - August to mid - October , while the fleet of Denmark , after two days ’ battle , compelled the Swedish fleet to abandon its projected attack on the Danish islands . The position of the Swedish king had now become critical . In July Denmark and Poland - Lithuania concluded an offensive and defensive alliance . Still more ominously for the Swedes , the elector of Brandenburg , perceiving Sweden ' s difficulties , joined the league against Sweden and compelled Charles to accept the proffered mediation of Oliver Cromwell , Coenraad van Beuningen and Cardinal Mazarin . The negotiations foundered , however , upon the refusal of Sweden to refer the points in dispute to a general peace - congress , and Charles received encouragement from the capture of Fredriksodde , 23 October - 24 , whereupon he began to make preparations for conveying his troops over to Funen in transport vessels . But soon another and cheaper expedient presented itself . In the middle of December 1657 began the great frost , which would prove so fatal to Denmark . In a few weeks the cold had grown so intense that the freezing of an arm of the sea with so rapid a current as the Small Belt became a conceivable possibility ; and henceforth meteorological observations formed an essential part of the strategy of the Swedes . March across the Belts . On 28 January 1658 , Charles X arrived at Haderslev in South Jutland . His meteorologists estimated that in a couple of days the ice of the Little Belt would become firm enough to bear even the passage of a mail - clad host . The cold during the night of 29 January became most severe ; and early in the morning of the 30th the Swedish king gave the order to start , the horsemen dismounting on the weaker spots of ice and cautiously leading their horses as far apart as possible , until they swung into their saddles again , closed their ranks and made a dash for the shore . Swedish arms quickly overpowered the Danish troops lining the opposite coast and won the whole of Funen with the loss of only two companies of cavalry , which disappeared under the ice while fighting with the Danish left wing . Pursuing his march , Charles X , with his eyes fixed steadily on Copenhagen , resolved to cross the frozen Great Belt also . However , he accepted the advice of his chief engineer officer Erik Dahlberg , who acted as pioneer throughout and chose the more circuitous route from Svendborg , by the islands of Langeland , Lolland and Falster , in preference to the direct route from Nyborg to Korsør , which would have had to cross a broad , almost uninterrupted expanse of ice . A council of war , which met at two o ’ clock in the morning to consider the practicability of Dahlberg ' s proposal , dismissed it as hazardous . Even the king wavered ; but when Dahlberg persisted in his opinion , Charles overruled the objections of the commanders . On the night of 5 February the transit began , the cavalry leading the way through the snow - covered ice , which quickly thawed beneath the horses ’ hoofs so that the infantry which followed after had to wade through half an ell of sludge , facing the risk that the ice would break beneath their feet . At three o ’ clock in the afternoon , with Dahlberg leading the way , the army reached Grimsted in Lolland without losing a man ; on 8 February , Charles reached Falster . On 11 February he stood safely on the soil of Zealand . A Swedish medal struck to commemorate the transit of the Baltic Sea bear the inscription : " Natura hoc debuit uni " . Sweden had achieved a rare war exploit , in Sweden considered to be matched only by the crusade of the Livonian Order led by William of Modena to conquer Saaremaa ( Osel ) in January 1227 and afterwards when two Russian armies crossed the frozen Gulf of Bothnia from Finland to mainland Sweden in March 1809 during the Finnish War . It is believed that the effect of this achievement on the Danish government found expression in the Treaty of Taastrup on 18 February , and in the Treaty of Roskilde ( 26 February 1658 ) , whereby Denmark sacrificed a great part of her territory to save the rest . However , Charles X continued the war efforts against Denmark after a council held at Gottorp on 7 July , even though he was in defiance of international equity . Without warning , Denmark was attacked a second time . On 17 July he again landed on Zealand and besieged Copenhagen with its king Frederick III of Denmark , but Copenhagen repelled a major assault and managed to hold out long enough for the Dutch fleet under Lieutenant - Admiral Jacob van Wassenaer Obdam to relieve the city , defeating the Swedish fleet in the Battle of the Sound on 29 October 1658 . Jutland had been reconquered by Denmark ' s allies , Poland and Brandenburg , and in 1659 Danish and forces liberated the Island of Funen in the Battle of Nyborg . As Baltic trade was vital to the Dutch economy they made clear to Charles they wouldn ' t allow Sweden to control the Sound . The Estates in Gothenburg . Charles X consented to reopen negotiations with Denmark , at the same time proposing to exercise pressure upon his rival by a simultaneous winter campaign in Norway . Such an enterprise necessitated fresh subsidies from his already impoverished people , and obliged him in December 1659 to cross over to Sweden to meet the estates , whom he had summoned to Gothenburg . The lower estates protested the imposition of fresh burdens , but were persuaded by Charles . Illness and death . Soon after the estates opened on 4 January 1660 , Charles X Gustav fell ill with symptoms of a cold . Ignoring his illness , he repeatedly went to inspect the Swedish forces near Gothenburg , and soon broke down with chills , headaches and dyspnoea . On 15 January , court physician Johann Köster arrived , and in medical error mistook Charles X Gustav ' s pneumonia for scorbut and dyspepsia . Köster started a " cure " including the application of multiple enemata , laxatives , bloodletting and sneezing powder . While after three weeks the fever eventually was down and the coughing was better , the pneumonia had persisted and evolved into a sepsis by 8 February . On 12 February , Charles X Gustav signed his testament : His son , Charles XI of Sweden , was still a minor , and Charles X Gustav appointed a minor regency consisting of six relatives and close friends . Charles X Gustav died the next day at the age of 37 . Family . Charles X had one legitimate child by Hedwig Eleonora of Holstein - Gottorp : his successor Charles XI ( 1655 – 1697 , reigned 1660 – 1697 ) . By Brita Allerts he had an illegitimate son : Gustaf Carlson ( 1647 – 1708 ) , who became Count of Börringe and Lindholmen Castle in Scania . He also had a number of other children , by different women , before his marriage .