The focal point of the city is the Detinets, or Kremlin. The chronicler first records it in the entry for 1044. In that year, ramparts with traditional wood framework constructions were built on the site of an elder fortification. The first stone structures appeared in 1302. According to Novgorodian chronicles, the towers and walls of the citadel underwent repeated repairs, and in 1484-90, during the all-round renovation of the fortress they were replaced with brick ones, erected in keeping with the traditions of Moscow architecture.

The present-day kremlin stems largely from the 15th century, for several alterations made in the 16th and 17th centuries were minor and did not affect its appearance. The total extension of the walls is 1,385 metres, they are 3.3 metres thick and 10.9 metres high. The area of the citadel is 12.1 hectares.