The Neo-Baroque domed structure is frequently mistaken for a part of the Peter and Paul Cathedral due to architectural similarities.
A covered passageway leads from the mausoleum to the cathedral, where the Russian emperors and empresses are buried.
It was constructed in order to remove the remains of some of the non-reigning Romanovs from the cathedral, where there was scarcely any room for new burials.
Antony Tomishko and Leon Benois were responsible for the actual construction work.
[1] The mausoleum was expected to hold up to sixty tombs, but by the time of the Russian Revolution there were only thirteen.