Principality of Smolensk
Mstislavl was first mentioned in the Ipatiev Chronicle under 1156. It was initially included within the Principality of Smolensk, but had become the capital of the Principality of Mstislavl by 1180. In the Middle Ages, it was the family seat of Princes Mstislavsky. Pyotr Mstislavets is believed to have been born in Mstislavl.