 On 20 June, a Swedish auxiliary expedition, dispatched already on 2 June, arrived with 600 men commanded by Colonel Fretz, Colonel James MacDougall and Major Semple.On 23 or 25 June, Stralsund concluded an alliance with Gustavus Adolphus of Sweden, scheduled to last twenty years.Gustavus Adolphus then stationed a garrison in the town, the first such on German soil in history.