The Jaromarsburg was a cult site for the Slavic tribe of Rani dedicated to the god Svantovit and used from the 9th to the 12th century. It was located on the northeastern tip of the Baltic Sea island of Rügen at Cape Arkona, and was protected on two sides by the cliffed coast and from the land side by a Slavic burgwall.
At Cape Arkona in recent centuries, sections of the cliff tops have continually collapsed into the sea, which is why the remnants of the Jaromarsburg today mainly comprise the castle ramparts. Based on a loss of 10 to 20 metres per century, it is believed that the current area within the ramparts represents only a third of the original total. As a result, for several years urgent archaeological excavations have taken place that have uncovered the site of the Svetovid temple, which had been thought for a long time had been lost to coastal collapse. It is a rectangular area that was completely free of artifacts, but to find around which, however, articles were discovered that may have been offerings, including parts of broken weapons. This is consistent with the historical account by Saxo Grammaticus, who states that the priests inside the temple were not even allowed to breathe within its confines, so as not to defile it.
The name of Jaromarsburg is derived from the Rani prince, Jaromar I. He became the only Rani prince of Rügen (Ruja, Rujána, Rána) after his brother Tetislav (last mentioned in 1170). He was a vassal of the Danish king, Valdemar I, because Rügen was conquered by Denmark in 1168. Due to that, the all old temples were destroyed and Rani were forced to convert to Christianity. The name Jaromarsburg is not used in the historical documents and was given to the burgwall later. In 1937 and 1938, a theory gained in popularity, that Jaromarsburg is a different spelling of Jomsburg, a lost Viking/Slavic city. It was supported by an information on a map from 17th century, that placed Jomsburg near to the cape Arcona. An archeological research had been done in the sea area but findings could not confirm the theory.