As one of the historical versions of Prince Vladimir in X. shown here in an inheritance to his son Izyaslav, according to another city was founded by Prince Izyaslav Mstislavovich in the XIII century. At the end of this century Izyaslav (throughout its history, also known as Izyaslavl, Zaslav, Zaslavl) is part of the Galicia-Volyn principality, and in the XIV century. it belongs to the princes Ostrozhsky. Then they were owned by the representatives of one of the branches of Ostrozkiy princes brothers, with whom in 1466 on the banks of the river erected a wooden castle, in 1539, replaced on the stone. Despite the frequent devastating Tatar raids Izyaslav gradually becoming a significant economic and trade center. After the Brest union in 1596 on the high left bank Horyn starts building huge Bernardine monastery, defense installations which have traditionally been written in the spectacular surrounding landscape.

In the monastery complex was composed of the Cathedral of St. John the Baptist (1599, architect J. de la Madeleine), St. Michael's Catholic Church (1602 architect J. de la Madeleine), and a huge cell quarters. And the castle and monastery buildings were substantially destroyed during the liberation war of Ukrainian people in 1648 and the castle remained in ruins and the monastery rebuilt and partially rebuilt (1756, architect P. Fontana). His defensive in nature, supported by 6-foot wall, was used by the Soviet prison system, which opened on the territory of the monastery colony of strict regime, which continues to work and now.

The middle of the XVIII century. Princes Sanguszko family marked an attempt to breathe life into a pretty shabby Tatar raids and peasant uprisings Izyaslav. They made for him by a Polish King Augustus III of Magdeburg Law (1754) and significantly changed the architectural appearance of the city. On the right bank Horyn was erected church of St. Joseph of the Order of Missionaries (1750-1760 gg., Architect P. Fontana), Bernardine monastery rebuilt and built the prince's palace complex, which to this day preserved skeleton of the palace and courtyard with arcades. In the XX century. decorated the city and the Orthodox Holy Trinity Church, located on the highest hill of the left bank Horyn and symbolic cut in Izyaslav-dominant for centuries in Catholic places of worship.