In 1710, the Swedish army in Poland retreated to Swedish Pomerania, pursued by the coalition. In 1711, siege was laid to Stralsund. Yet the town could not be taken due to the arrival of a Swedish relief army, which secured the Pomeranian pocket before turning west to defeat an allied army in the Battle of Gadebusch. Pursued by coalition forces, the Swedish army was trapped and surrendered in the Siege of Tönning. In 1714, Charles XII returned from the Ottoman Empire, arriving in Stralsund in November. In nearby Greifswald, already lost to Sweden, Russian tsar Peter the Great and British king George I, in his position as Elector of Hanover, had just signed an alliance on 17 /28  October. Previously a formally neutral party in the Pomeranian campaigns, Brandenburg-Prussia openly joined the coalition by declaring war on Sweden in the summer of 1715. Charles was then at war with much of Northern Europe, and Stralsund was doomed. Charles remained there until December 1715, escaping only days before Stralsund fell. When Wismar surrendered in 1716, all of Sweden's Baltic and German possessions were lost.. Where did Peter the Great and George I sign the alliance?