Oster was founded in 1098 by Vladimir II Monomakh as Gorodets, a fortress belonging to the Pereiaslav principality, which was later inherited by his son Yuri Dolgorukiy.
The town of Oster originated in 1098 when Vladimir II Monomakh founded it as Gorodets, a fortified settlement within the Pereiaslav principality, which was subsequently taken over by his son Yuri Dolgorukiy.