The Polish–Swedish War of 1626–1629 was the fourth stage (after 1600–1611, 1617–1618, and 1620–1625) in a series of conflicts between Sweden and Poland fought in the 17th century. It began in 1626 and ended four years later with the Truce of Altmark and later at Stuhmsdorf with the Treaty of Stuhmsdorf. Course 1626 The first encounter of the war took place near Wallhof, Latvia, where a Swedish army of 4,900 men under Gustavus II Adolphus ambushed a Polish-Lithuanian force of 2,000 men under Jan Stanisław Sapieha. Polish-Lithuanian casualties amounted to between 500 and 1000 dead, wounded and captured. The Lithuanian commander later suffered a nervous breakdown. In May 1626 King Gustavus Adolphus launched his invasion of Polish Prussia. Escorted by a fleet of over 125 ships, Swedish forces numbering over 8,000 soldiers (including 1,000 cavalry) disembarked in Ducal Prussia near Piława (Pillau). The landings were a complete surprise to the Polish–Lithuanian Commonwealth's defences, and despite his relatively small forces, Gustavus Adolphus quickly captured 16 Prussian towns, almost without a fight (with the neutral Duchy of Prussia's passive support). Many of these towns were inhabited by Protestants and they opened their gates freely to the Lutheran Swedish forces, who they saw as co-religionists. The Swedish king, however, failed to capture the largest prize - the city of Danzig (Gdańsk), which maintained its own small army and fleet for defence. In preparation for his major attack on Danzig, King Gustavus Adolphus increased his forces to over 22,000. The Polish king, Sigismund III, received no support from his vassal, Ducal Prussia, when fighting to defend it. He deployed north with an army of 11,000 men and pitched battle at Gniew against King Gustavus Adolphus' force of 8,150 infantry, 1,750 cavalry and 74 cannon. The fighting continued for several days - from 22 September to 1 October 1626 - until Sigismund III withdrew his army, and called on reinforcements from around the country. The Polish hetman (historical army rank equivalent to field marshal) Stanisław Koniecpolski quickly came to his king's aid with a force of 4,200 light cavalry, 1,000 dragoons, and 1,000 infantry. In early November the king handed him command of the army. With further reinforcements Koniecpolski soon had 10,000 men to match the 20,000 Swedish troops in Prussia. Engaging in a war of maneuver - small mobile units striking at the enemy's lines of communication - Hetman Koniecpolski managed to halt any