Pereiaslav or Pereyaslav (, ; ), formerly Pereiaslav-Khmelnytskyi or Pereyaslav-Khmelnytskyy (1943–2019), is a historical city in the Boryspil Raion, Kyiv Oblast (province) of central Ukraine, located near the confluence of Alta and Trubizh rivers some south of the nation's capital Kyiv. Along with Kyiv and Chernihiv, it forms the nucleus of the medieval Ruthenia. Pereiaslav hosts the administration of Pereiaslav urban hromada, one of the hromadas of Ukraine. Its population is approximately With its current estimated population about 30,000, and more than 20 museums, Pereiaslav is often described as a "living museum" and granted status of a History and Ethnography Reserve (). History Kievan Rus' 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-Rus'kyi (Pereyaslav Ruthenian/Pereyaslav Russiae), to distinguish it from Pereslavets in Bulgaria, later with establishment cities in Zalesye, from Pereslavl-Zalessky and Pereyaslavl Ryazansky. Vladimir I, Prince of Kiev built here in 992 the large fortress to protect the southern limits of Kievan 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'. Lithuania and Poland During the 14th century Pereiaslav was annexed by the Grand Duchy of Lithuania. Since 1471 it was part of the Kiev Voivodeship, which in 1569 became part of the Crown of the Kingdom of Poland. In 1585, Polish King Stephen Báthory granted Perejasław Magdeburg city rights. It was a royal city of Poland. Cossack Ukraine During the second half of the 16th century Pereiaslav became a regimental city of the Ukrainian Cossacks. Here in 1654 Bohdan Khmelnytsky had the controversial "Pereiaslav Convent", where the Ukrainian Cossacks had voted for a military alliance with Muscovy and accepted the Treaty of Pereyaslav. The treaty resulted in the establishment of the Cossack Hetmanate in left-bank Ukraine subject to the Tsardom of Russia, and to the Russo-Polish War (1654-1667). The town known as Pereiaslav at that time, and later as Pereiaslav-Poltavskyi. According to the Truce of Andrusovo in 1667, Pereiaslav became part of Russia. Soviet museum center Upon the end of World War II, the Soviet government, keen to glorify the Treaty of Pereiaslav as the ground for Ukraine's unification with