Pereiaslav played a significant role in the history of Ukraine. It was mentioned for the first time in the text of the Rus' treaty with the Byzantine Empire (911) as Pereyaslav-Ruskyi, to distinguish it from Pereyaslavets in Bulgaria. Vladimir I, Prince of Kiev built here in 992 the large fortress to protect the southern limits of Kyivan Rus from raids of nomads from steppes of what is now southern Ukraine. The city was the capital of the Principality of Pereiaslavl' from the middle of the 11th century until its demolition by Tatars in 1239, during the Mongol invasion of Kievan Rus'.