The siege of Stralsund was a battle during the Great Northern War. The Swedish Empire defended her Swedish Pomeranian port of Stralsund against a coalition of Denmark-Norway, the Electorate of Saxony and the Tsardom of Russia, which was joined by the Kingdom of Prussia during the siege.
A first attempt to take Stralsund was made in 1711, when the allies closed in on the town. Swedish relief forced the coalition to withdraw from the fortifications, whereupon the besieging armies drew a wider ring along the lines of the Recknitz and Peene rivers. Magnus Stenbock's victory at Gadebusch for a short time distracted the allies, but after Stenbock's pursuit and subsequent defeat, Prussia as well as Hanover, ruled in personal union with Great Britain, joined the anti-Swedish alliance.
The allies agreed that Denmark should cede her claims to Bremen-Verden to Hanover, and in turn Denmark was promised the northern parts of Swedish Pomerania with Stralsund, while the southern parts were to become Prussian. In 1714, Charles XII of Sweden rode to Stralsund from his Turkish exile to lead the defense in person. From 12 July to 24 December 1715, the allies sieged the town and eventually forced its surrender. Charles XII escaped to Sweden.
Stralsund remained under Danish control until it was returned to Sweden by the Treaty of Frederiksborg.
Prelude
In Poltava, the Swedish Empire lost the initiative in the Great Northern War. With Charles XII of Sweden's main army destroyed, the anti-Swedish alliance of the Tsardom of Russia, Denmark-Norway and Saxe-Poland-Lithuania re-constituted in the Treaty of Thorn and the Treaty of Copenhagen, the Swedish king exiled to Bender and Sweden's provinces of Finland and Livonia invaded, the Swedish defense relied on 11,800 soldiers garrisoned in northern Germany, and an army of 10,000 men in Greater Poland commanded by Ernst Detlof von Krassow. The latter was in full retreat, harassed by Saxon forces and a plague that had broken out in Poland.
The Swedish government issued mobilization orders for Swedish Pomerania on 8 April 1711. 3,800 men aged between twenty and forty years were to be drawn to serve a five years term. Stralsund had recovered from the destruction of 1678, but in 1711, the plague carried to Pomerania with the retreating Swedish forces of the Krassow corps caused thousands of deaths. The Swedes were pursued by the armies of the anti-Swedish coalition, who reached and laid siege to Stralsund in 1711.
This pursuit through formerly neutral Reich territory was made possible by the death of emperor Joseph I in April: until Joseph I's successor Charles VI was inaugurated, the imperial constitution ruled that August the Strong, one of the constituents of the anti-Swedish coalition, was in charge of northern Germany's imperial affairs. Thus, when the Swedish forces withdrew to their fortified strongholds of Stralsund, Stettin (Szczecin) and Wismar, 6,000 Saxons, 6,000 Poles, and 12,000 Russians were able to follow up from the southeast. Another 25,000 Danes moved into the empire via Holstein-Gottorp, and approached Stralsund from the west.
Siege
A Swedish relief force under Magnus Stenbock's command with a strength of 6,000 to 10,000 men landed on Rügen on 25 September 1711, whereupon the Danish-Saxon-Russian siege army withdrew to the Recknitz and Peene rivers. Instead of a launching another major assault on the town, the allies were content with minor raids and skirmishes into the pocket in the following years. Swedish general Carl Gustaf Dücker requested reinforcements, and in May 1712 was supplied with an additional 6,391 foot and 4,800 horse from Sweden. Also, Dücker concentrated all Swedish forces scattered in Pomeranian garrisons, another 8,000 men, in Stralsund, while the allied strength was about 23,000 men.
At this time, Frederik IV of Denmark-Norway was not interested in annexing Stralsund to his empire. When he re-entered the war in 1709, Frederik had promised to not attack Swedish territories in the Holy Roman Empire and protect their citizens wherever they pledge loyalty to him. Accordingly, Frederik IV had agreed in a convention of 1711 that Stralsund along with northern Swedish Pomerania should be annexed by August the Strong, elector of Saxony and king of Poland-Lithuania. However, after George I of Brunswick-Lüneburg (Hanover) ascended the throne of Great Britain, who had dropped out of the War of Spanish Succession in the Peace of Utrecht in 1713 and was thus free to enter the anti-Swedish alliance in the Great Northern War, Frederik IV changed his mind. Already in 1712, Denmark and Hanover had invaded and partitioned Bremen-Verden.