The fortress that held out against Wallenstein’s siege in 1628 was Stralsund. The strategically important Baltic port was an independent Hanseatic city in Pomerania, and it refused to accept Imperial troops after the duchy capitulated to the Holy Roman Empire.
Wallenstein’s forces began the siege in May 1628. Stralsund received reinforcements from Denmark, Scotland, and Sweden, including troops commanded by Alexander Leslie. Despite repeated assaults and heavy casualties, the defenders kept control of the city’s fortifications.
Wallenstein personally took command during the siege, but he lifted it on 4 August 1628. The failure ended his run of victories and gave Sweden a valuable bridgehead on the southern Baltic. Gustavus Adolphus later used Stralsund as a base for Sweden’s intervention in the Thirty Years’ War.
A common mix-up is confusing Stralsund with nearby Pomeranian towns involved in the wider campaign. The city’s resistance mattered because controlling it would have strengthened Imperial power along the Baltic coast.