The Peter and Paul Fortress (Russian: Петропа́вловская кре́пость, also Fortress of SS Peter and Paul) is the original citadel of St. Petersburg, Russia, designed by Domenico Trezzini and founded in 1703. The fortress contains a number of buildings including the Peter and Paul Cathedral, where all Russian tsars from Peter I to Alexander III are interred; the remains of the Imperial martyrs, Nicholas II and his family and entourage, were also interred there, in the side St.Catherine's Chapel, on the 80th anniversary of their deaths, July 17, 1998. Towards the end of 2006, the remains of Dowager Empress Maria Feodorovna, mother of the murdered Nicholas II, who died in 1928 were brought from Roskilde Cathedral outside Copenhagen, Denmark to finally rest next to her husband, Alexander III.

      The fortress was established by Peter the Great on May 16 (by the Julian Calendar, May 27 by the Gregorian Calendar) 1703 on a small island, Zayachii (hare) (or Vesiolii - cheerful) ostrov, on the Neva River. Built during the Northern War, the fort was never actually needed. The fort was completed with six bastions in earth and timber within a year, it was rebuilt with stone from 1706 to 1740. From around 1720 the fort served as a base for the city garrison and also as a prison for high ranking or political prisoners. The Trubetskoy bastion, built in the 1870s, became the main prison block. The Cathedral was built from 1712 to 1733, and has a 123.2 m bell-tower and a gilded angel-topped cupola.