Nestor in the Primary Chronicle mentions Slavic tribes, the Tivertsi and Ulichs along the Dniester. The Avars invaded in the 7th century. Prince Oleg of Kiev, extended his rule over this territory known as the "ponizie", or "lowlands." In the 13th century, the Mongols plundered Ponizie; Algirdas, prince of the Grand Duchy of Lithuania, freed it from their rule following his victory against the Golden Horde in the Battle of Blue Waters of 1362, annexing it to his own territories under the name of "Podolia", which means "ponizie", and Polish colonization began in the 14th century.