The Polish–Swedish War of 1621 to 1625 was a war in a long-running series of conflicts between the Polish–Lithuanian Commonwealth and the Swedish Empire. It began with a Swedish invasion of the Polish–Lithuanian fiefdom Livonia. Swedish forces succeeded in taking the city of Riga after a siege. The Commonwealth, focussed on war with the Ottoman Empire (such as the battles of Cecora and Chocim), was unable to send significant forces to stop Gustav Adolf, and signed a truce favorable to Sweden. The Commonwealth ceded Livonia north of the Dvina (Düna) river, and retained only nominal control over Riga. The new truce in Mitau (Jelgava, Mitawa) was signed and lasted from November 1622 to March 1625. Introduction The Polish–Swedish War of 1617–18) showed that the Swedish Army, despite several reforms, was still unable to defeat the Polish–Lithuanian Commonwealth. Furthermore, King Gustav Adolf was still regarded in Europe as a usurper. To safeguard the Swedish crown for himself, Gustav Adolf decided to force Sigismund III Vasa to relinquish it. With help from Axel Oxenstierna, the Swedish king introduced a widespread program of military and social reforms, which resulted in creation of a well trained army, based on native recruits. These further reforms and the ongoing conflict between the Commonwealth and the Ottoman Empire (see Polish–Ottoman War (1620–21)), offered Gustav Adolf a further chance to defeat the Commonwealth. First phase (1621–22) While the Polish–Lithuanian army was concentrated in Podolia, in the south of the Commonwealth, a Swedish army landed near Pärnu (today part of Estonia) on 19 August 1621. It was carried by a fleet of 148 vessels (25 warships, 3 pinnacles, 7 galleys, 7 smaller warships and 106 transport boats). Gustav Adolf had 14,700 infantry, 3,150 cavalry and 375 cannons. The Swedes immediately marched towards Riga, and started a siege on 29 August. The capital of Livonia was defended by a garrison of 300 soldiers, plus 3,700 armed residents. Lithuanian Field Hetman Krzysztof Radziwiłł had only 1,500 soldiers at his disposal, as most units were in Podolia and Red Ruthenia. Riga capitulated on 25 September, after three assaults. On 2 October the Swedes captured the fortress of Dunamunde. The invaders, marching through marshes and forests to avoid Lithuanian cavalry, entered the Duchy of Courland and Semigallia, capturing its capital, Mitau without resistance. The Swedes then tried to capture the fortress of Koknese, but failed to do so, after a skirmish with Lithuanian