Saint Basil's Cathedral, which delimits the square on the south side, is undoubtedly the most famous building from the Red Square ensemble and is considered one of Moscow's landmarks. Her full name is actually Cathedral of the Protection and Intercession of the Virgin Mary. Once it was the main place of worship in the Tsar's capital, today the main function of the cathedral is a museum that is part of the complex of the State History Museum opposite. Since the beginning of the 1990s, services have also been held in St. Basil's Cathedral at irregular intervals.