Älvsborg fortress Älvsborg , also Elfsborg Fortress , is a large sea fortress in Rivö fjord , within modern Gothenburg , Sweden . Situated at the mouth of the Göta River , it served to protect medieval Sweden ' s only access to the North Sea and Atlantic Ocean and the nearby settlement of today ' s Gothenburg and its four predecessors ( Lödöse , Nya Lödöse , Älvsborg and Charles IX ' s Gothenburg ) . The original Old Älvsborg Fortress ( or " Älvsborgs slott " ) was located on the mainland , on the southern shore of the estuary , above modern Klippan . Only few ruins are visible today in the vicinity of the Carnegie - pier . The old fortress was dismantled and relocated to one of the islands in the estuary , in the 17th century . This New Älvsborg Fortress ( ) is still maintained . In 1643 , a settlement in New Sweden , North America , was named Fort Nya Elfsborg ( " Fort New Älvsborg " ) , after the Swedish fortress . This settlement was abandoned in 1655 . Gothenburg was the main centre for Swedes emigrating to America , and the fortress would have been one of the last sights the emigrants saw on leaving the country . Old Älvsborg Fortress . A fortified outpost was especially important for Sweden when the area north of Älvsborg , Bohuslän , was part of Norway ( until 1658 ) , and the area south of it , Halland , was part of Denmark ( until 1645 ) . Sweden ' s only Atlantic settlement , Gothenburg ' s first predecessor Lödöse ( " Gothenburg 1 " ) at the mouth of the Göta Älv , was built about 1200 , superseded by New Lödöse ( " Gothenburg 2 " ) near the modern town . In 1473 , New Lödöse was granted substantial privileges . The Old Älvsborg Fortress was built in the 14th century , located at the Klippan area near what is now the harbour entrance of Gothenburg . After the Danes several times easily conquered the fortress , the fortification works was gradually expanded . New Lödöse was burned down by Danish forces in 1521 , and after it was initially rebuilt at the same spot in 1526 , it was later relocated ( " Gothenburg 3 " ) near the Älvsborg fortress , west of the modern town . In 1563 , when the Northern Seven Years ' War broke out , the Swedish burned down this town by themselves to not let Denmark capture it , and Denmark took over Älvsborg Fortress . The war ended with the Treaty of Stettin ( 1570 ) , which obliged Sweden to pay 150 , 000 " riksdaler " for the ransom of the fortress of Älvsborg . To pay this extraordinarily high amount of money , Sweden heavily taxed all moveables in the country , resulting in further impoverishment of the war - torn population . Unburned towns had to pay one twelfth , peasants one tenth , burned down towns one eighteenth of their properties ' value . In 1603 , the adjacent town was again relocated ( " Gothenburg 4 " ) to the site of the channel opposing Älvsborg Fortress , it was the first town called " Göteborg " , built by Charles IX of Sweden . The town was annilihated by Denmark in 1611 , who took possession of Älvsborg between 1612 and 1619 . Today , only few remains of the fortress are preserved , located at . New Älvsborg Fortress . New Älvsborg Fortress was built in the 17th century near the ruins of the old fortress , but on a small island where the Göta Älv river meets the sea . It protected the new town of Gothenburg , founded in 1621 by Gustavus Adolphus of Sweden . New Älvsborg Fortress today is a listed building ( " byggnadsminne " ) and a popular tourist attraction .