Jersika or Gercike (, , also known as Berzika in the Middle Ages) was a centre of the early medieval Principality of Jersika. Today Jersika is a historical hillfort in Latvia, southeast of Riga.

History

Jersika was established in 10th century as an outpost of the Principality of Polotsk on the old "trade route from the Varangians to the Greeks". It was ruled by Eastern Orthodox princes from the Latgallian-Polatsk branch of the Rurik Dynasty.

In 1209 Visvaldis, the Prince of Jersika, was militarily defeated by Bishop Albert of Riga, and his Lithuanian wife taken prisoner. He was forced to submit his kingdom to Albert as a grant to the Bishopric of Riga, and received back only a portion of it as a fief. Visvaldis' feudal charter is the oldest such document surviving in Latvia, and in this charter Visvaldis is called "the King of Jersika"—"Vissewalde, rex de Gercike" (in another document also "Wiscewolodus rex de Berzika") .

In 1211 the part of Jersika known as "Latvia" ("terra, quae Lettia dicitur"), and which was controlled by Albert, was divided between Bishopric of Riga and Livonian Brothers of the Sword.

After the death of Visvaldis in 1239 his fief passed to the Livonian Order, but this was repeatedly contested by the princes of Lithuania and Novgorod, who periodically sought to conquer the territory.