Jomsborg or Jómsborg (German: Jomsburg) was a semi-legendary Viking stronghold at the southern coast of the Baltic Sea (medieval Wendland, modern Pomerania), that existed between the 960s and 1043. Its inhabitants were known as Jomsvikings. Jomsborg's exact location, or its existence, has not yet been established, though it is often maintained that Jomsborg was somewhere on the islands of the Oder estuary. Lauritz Weibull dismissed it as a legend.
Jomsborg is often thought to be identical with the present-day town of Wolin (also Wollin) on the southeastern tip of the isle of Wolin, probably located at Silberberg hill north of the town. In the Early Middle Ages, modern Wolin was the site of a multi-ethnic emporium (then known as Jumne or Julin). The Nordic sagas use "Jómsborg" exclusively, while medieval German histories use "Jumne" or "Julin", with the alternate names, some of which may be spelling variants, "vimne", "uimne", "Jumneta", "Juminem", "Julinum", "uineta", "Vineta" and "Vinneta". In 1931/32, Pomeranian historian Adolf Hofmeister suggested, through comparison of the events reported by the different chronicles, that all these terms describe the same place, which is at or near the modern town of Wolin. However, this is by no means universally accepted; Steven Fanning writes: "The Trelleborg-type fortresses of Denmark have been taken to be actual examples of Jómsborg-style camps of such warriors and Wolin in Poland was believed to be the actual Jómsborg. However, all such attempts to locate Jómsborg or encampments of the Jómvikings have failed, leading many to doubt that Jómvikings ever existed outside of literature." According to Władysław Filipowiak there are several dated sources which attest to the presence of a company of armed Vikings at the end of the 10th century in Wolin, who may have been installed there as mercenaries by the Polish king Bolesław Chrobry.
Other theories see Jomsborg in the northwest of nearby Usedom island, on lands now submerged. The small islands in this area are remnants of a long stretch of land between Usedom and Rügen, which fell victim to storm floods in the early 14th century. Suspected locations in this area are the Veritas grounds between the petty islands of Ruden and Greifswalder Oie, and the Peenemünde shoals. While Viking Age jewelry has been found at the site, archaeological evaluation of these theories has not yet been possible.
The fortress 
According to the Knytlingasaga and Fagrskinna, Jomsborg was built by the Danish king Harold Bluetooth (910-985/86) in the 960s. The Jomsvikinga Saga mentions Danish Viking Palnatoki as its founder.
In medieval records, Jomsborg is described as a fortress with a harbour. The harbour was overseen by a stone tower mounted with catapults, built on an arch spanning over the harbour entrance which could be closed by an iron gate. According to the oldest records, the harbour had space for three ships, later records give a capacity of up to 360 ships.
Most records name the jarl of Jomsborg Sigvald(i), son of petty king Strut-Harald of then Danish Scania. Sigvald died some time before 1010. The Jomsborg Vikings (Jomsvikings) were composed of selected warriors, adhered to a special codex, and were loyal only to their leader. In 1009, many Jomsvikings left Jomsborg and followed Sigvald's brothers Herring and Thorkell the Tall to England, where they became the nucleus of Cnut the Great's Thingmen or Huscarls.
Historical events involving Jomsborg 
- Styrbjörn the Strong and a force of Jomsvikings departed from Jomsborg to reclaim the Swedish throne from Eric the Victorious, yet were defeated in Fyrisvellir near Gamla Uppsala in the late 980s.
- Sweyn Forkbeard and a force of Jomsvikings departed from Jomsborg to eliminate jarl Haakon Sigurdsson of Norway, but were defeated in the Battle of Hjörungavágr (~990).
- Olaf I of Norway and a Jomsviking contingent departed from Jomsborg for the Battle of Svolder in 999 or 1000 AD.
See also 
- T. D. Kendrick, A History of the Vikings, Courier Dover Publications, 2004, pp.179ff, ISBN 048643396
- T. D. Kendrick, A History of the Vikings, Courier Dover Publications, 2004, p.179, ISBN 048643396
- Jan M Piskorski, Pommern im Wandel der Zeit, 1999, p.31, ISBN 839061848
- Johannes Hoops, Herbert Jankuhn, Heinrich Beck, Reallexikon der germanischen Altertumskunde Band 16, 2nd edition, Walter de Gruyter, 2000, pp.120-121, ISBN 3-11-016782-4
- Steven Fanning, "Tacitus, Beowulf, and the Comitatus," Haskins Society Journal 9 (1997), 30–31.
- Filipowiak, Władysław (2004). "Some aspects of the development of Wolin in the 8th-11th centuries in the light of the results of new research". In Przemysław, Urbanczyk. Polish lands at the turn of the first and the second millenium. Institute of Archeology and Ethnology. Polish Academy of Sciences. pp. 47–74.
- T. D. Kendrick, A History of the Vikings, Courier Dover Publications, 2004, p.180, ISBN 048643396
- Ingrid Lange, Paul Werner Lange, Vineta, Atlantis des Nordens, Urania, 1988, p.120, ISBN 3-332-00197-3
- T. D. Kendrick, A History of the Vikings, Courier Dover Publications, 2004, p.181, ISBN 048643396
- R. Chartrand, Magnus Magnusson, Ian Heath, Mark Harrison, Keith Durham, The Vikings: Voyagers of Discovery and Plunder, Osprey Publishing, 2006, p.88, ISBN 1-84603-087-0
- R. Chartrand, Magnus Magnusson, Ian Heath, Mark Harrison, Keith Durham, The Vikings: Voyagers of Discovery and Plunder, Osprey Publishing, 2006, p.89, ISBN 1-84603-087-0
- R. Chartrand, Magnus Magnusson, Ian Heath, Mark Harrison, Keith Durham, The Vikings: Voyagers of Discovery and Plunder, Osprey Publishing, 2006, p.90, ISBN 1-84603-087-0
- R. Chartrand, Magnus Magnusson, Ian Heath, Mark Harrison, Keith Durham, The Vikings: Voyagers of Discovery and Plunder, Osprey Publishing, 2006, p.91, ISBN 1-84603-087-0
- T. D. Kendrick, A History of the Vikings, Courier Dover Publications, 2004, p.182, ISBN 048643396