Rewel (Tallinn) w planach Zygmunta Augusta

Reval city (modern Tallinn) in the middle of the 16th c. was one of the largest cities of Livonia. This important seaport, which played a key role in the Hanseatic trade with Russia, consisted of a strongly fortified city and castle. After invasion of the army of Ivan the Terrible into Livonia in 1558, the residents of Reval – facing the weakness of the Livonian Order – quickly felt the threat of a violent aggressor. Looking for help from neighboring countries, the authorities of Reval turned to Sweden and Denmark for help but were not granted any support. The situation changed when in the Livonian conflict became involved King Sigismund Augustus, who strived to rule the whole Livonian lands. He appreciated the importance of Reval city as the most important port on the northern Livonia, enabling rapid delivery of food, weapons and soldiers for fighting. Involved in the diplomatic game Sigismund Augustus missed most convenient moment to get control over Reval city. The moment was seized by the new king of Sweden, Erik XIV Vasa, who in 1561, conquered Reval and a portion of Harrien (Harju) and Wierland (Virumaa). Action taken by Sigismund Augustus, to get control over Reval, did not bring the expected results, also due to the reluctance of the authorities and inhabitants of the city to pass under the rule of Lithuania. Struggling with financial problems Polish king ultimately failed to recover Reval through diplomatic negotiations (Szczecin Congress in 1570), as well as, by force. The loss of Reval city and acceptance of the Swedish rule over a large part of the Estonia must be regarded as one of the most important errors of King Sigismund Augustus, resulting in the loss of the greater part of the Livonian lands.