In 1659, the war was characterized by Swedish forces defending their strongholds on the southern Baltic coast against allied assaults. A combined force of 17,000 Austrians and 13,000 Brandenburgers led by general Jean-Louis Raduit de Souches invaded Swedish Pomerania, took and burned Greifenhagen, took Wollin island and Damm, besieged Stettin and Greifswald without success, but took Demmin on 9 November. Counterattacks were mounted by general Müller von der Lühnen, who lifted the siege laid on Greifswald by the Brandenburgian prince elector, and major general Paul Wirtz, who from besieged Stettin managed to capture the Brandenburgian ammunition depot at Curau and took it to Stralsund. The Brandenburgians withdrew ravaging the countryside while retreating. In the occupied and annexed Danish provinces, guerilla movements pressed Swedish garrisons. After an uprising, Norwegians took Trondheim in late 1658. In Scania and Zealand, the "snaphaner" led by Lorenz Tuxen and Svend Poulsen  ambushed Swedish forces. The Swedish garrison of Bornholm was forced to surrender to Danish insurgents, with the commander killed. In Royal Prussia , Thorn had fallen already in December 1658, but Elbing and Marienwerder withstood. On 24 November, Sweden had to abandon Funen and Langeland after the defeat in the Battle of Nyborg. In January 1660, Sweden lost the Livonian fortress Mitau. Meanwhile, conflicts arose within the anti-Swedish alliance between Habsburg and Poland-Lithuania when Habsburg demanded ever more contributions while not showing the war efforts Poland-Lithuania had expected. With the Russo-Polish War ongoing, most Polish-Lithuanian forces were bound in Ukraine. England, France and the Dutch Republic had agreed on a petition in the First Concert of the Hague, urging Sweden to settle for peace with Denmark on the terms of Roskilde, and peace talks mediated by France were taking place throughout 1659.
Question: What two cities could not be successfully sieged?
Answer: Stettin and Greifswald