According to the chronicle, the Truvor Gorodishche was founded by Truvor, the brother of Ryurik, and Izborsk, which was originally called Slovensk, was one of the main centers of the Slavic tribe of Kryvychi.
By the 11 century the medieval proto-town of the Kryvychi, Izborsk, was rather big, but the Truvor Gorodishche remained the main citadel in its center. But it was too small and could not withstand long sieges. The Livonian Knights captured Izborsk two times, in 1233 and in 1240. By that time Pskov was a town with strong defensive system. As a result, Izborsk lost its political influence, but remained very important as regards to the defense of Pskov lands.
In 1302 the Izborsk fortress was moved in a more advantageous place on the Zheravya Gora, one and a half kilometers from Truvor`s Gorodishche. At first the fortress was wooden, but soon the stone Lukovka tower (main tower of the fortress) was built, and in 1330 the Pskov posadnik Sheloga had the entire fortress enclosed by stone walls.
Most of the structures inside the Izborsk fortress, excepting the St. Nicholas cathedral, an example of the early Pskov architecture, were lost. It is considered that the church was built at the beginning of the 14 century, but the first records of it dates back only to 1341.
For a long time the Izborsk fortress had a great defensive value on the western border of Pskov lands and was the first to face enemy attacks. The stone fortress withstood 8 attacks but was not captured by the enemy troops. With the development of artillery the walls were strengthened and made thicker. In places the thickness of walls reached 5 meters, but by the beginning of the Great Northern War of the 18 century, Izborsk did lost its military importance.