Rethra (also known as Radagoszcz, Radegost, Radigast, Redigast, Radgosc and other forms like Ruthengost) was, in the 10th to the 12th centuries, the main town and political center of the Slavic Redarians, one of the four major Lutician tribes, located most likely in present-day Mecklenburg.
[5] Radagosc is described in the chronicles of Thietmar of Merseburg, who used the name Riedegost, while, writing about fifty years later, Adam of Bremen referred to it as Rethra.
[13] This is in part because the main deity worshiped in Riedegost/Rethra was reported as Zuarasici (Swarożyc) by Thietmar (VI, 23), and as Redigost (Redigast, Riedegost) by Adam of Bremen (II, 21; III, 51) as well as the 12th century chronicler Helmold (I, 2).
[15] In Slavic languages, the suffix "-yc","-ič", "-wicz", "-vič" added to a personal name creates a patronym, meaning a "son", or more generally "offspring" or "descendant" of the person bearing the name, therefore Svarožič, or Swarożyc is "a son", "grandson" or other offspring of Svarog (with "g" replaced with "ż", or "ž", according to Slavic grammar rules).
Likewise the successful beginning of the Obotrite revolt of 1066 was, according to Adam of Bremen celebrated in "Rethra" by the ritual decapitation of captured bishop Johann of Mecklenburg and the sacrifice of his head, stuck on a lance, to Riedegost.
[16] The last historical record of "Rheda" is an entry in the Annals of Augsburg for the year 1068,[16] describing its capture by bishop Burchard and the abduction of its sacred horse.