Saint Petersburg is a relatively recent city. As it was founded by Tsar Peter the Great in 1703 there aren’t any buildings over 300 years old. The Kazan Cathedral was built in 1800, but had to resemble the St Peter’s Basilica in Vatican City. This meant that it had to look old as well. Because of this old stones were imported to built the cathedral. So actually the Kazan is a relatively new cathedral in an old coat.
This contrasts nicely with the new limo parked in front of it for the Easter celebration last week.