The second-class fortresses are Kronstadt and Sveaborg in the Gulf of Finland, Ivangorod in Poland, Libau on the Baltic Sea, Kerch on the Black Sea and Vladivostok on the Pacific. In the third class are Viborg in Finland, Ossovets and Ust Dvinsk (or Dunamunde) in Lithuania, Sevastopol and Ochakov on the Black Sea, and Kars and Batum in Caucasia.
The Lettish Government decided to stop the advance on Dvinsk and Rezhitsa at any cost, as a danger to Latvia's independence, and succeeded in obtaining British and Esthonian support.
Dvinsk was taken by the Poles, and Rezhitsa (the main town of Latgalia) by the Landeswehr, who advanced to Rozhanova.
Hostilities had already begun with the occupation of Diinaburg (Dvinsk) in Polish Livonia by the Swedes (July 1, 1655), and the Polish army encamped among the marshes of the Netze concluded a convention (July 25) whereby the palatinates of Posen and Kalisz placed themselves under the protection of the Swedish king.
A little more than twelve months later, a coup d'etat placed the tsesarevna Elizabeth on the throne (December 6, 1741), and Ivan and his family were imprisoned in the fortress of Diinamtinde (Ust Dvinsk) (December 1 3, 1742) after a preliminary detention a Riga, from whence the new empress had at first decided to send them home to Brunswick.