I think the image is flopped--check inscription over door.

Commissioned by Alexander I and dedicated to Saint Isaac of Dalmatia, a patron saint of Peter the Great who had been born on the feast day of that saint. William Handyside contributed engineering, as the marshy site had to be shored up with thousands of wooden piles. The cathedral has a symbolic role linked to the idea of Russia as the 'Third Rome'. Thus, despite the compact volume, the fact that the main façades are on the long north and south sides, and the five cupolas traditional on Russian cathedrals, there is a strong resemblance to St. Peter's, Rome, and its descendants, including St. Paul's Cathedral, London, and Les Invalides, Paris.