In the ХІІІ century, the city occupied an area of 3.5–4 ha and consisted of an inner city and settlement. The inner city is made up of the central fortified part located on a cape at the confluence of the Zachodni Buh and Muchaviec rivers and a circular city or settlement on a natural island formed by the distributaries of the Muchaviec.
The inner city was well fortified. Defence measures and natural barriers were primarily used – the large expanses of the Zachodni Buh and Muchaviec rivers. Artificial defenses were moats and ramparts with wooden buildings, and a defensive wall with a fighting gallery and watchtowers. To increase the city's defensive capacity, with the aim of good vision of the surrounding areas, in the second half of the ХІІІ century, a brick defensive tower was built, with a height of over 29 metres. According to chronicles, the Orthodox Church of St. Peter was built in Biarescie at the same time.