The oldest monument of history and architecture in St.-Petersburg.
  The construction of it started in 1703. It was built as a fortification during the Russian-Swedich war. But it was never used as a fortress and its bastions were turned into political prison sells. There a son of Peter the Great, prince Alexei, a famous pretender to the throne, princess Karakhakova, writer Radishchev, Decembrists, narodniks and revolutionaries were held prisoners.
 The Peter and Paul Cathedral designed by Tresini was the Buiral-vault of Russian emperors since 1725.