It’s most likely a reference to the Third Rome narrative, which argues that if the Roman Empire was “First Rome” and the Byzantines (note, not the HRE) were “Second Rome,” then Russia was the direct inheritor to their power and legitimacy.

u/VladtheWallachian and u/DarkTowersWeTrust explain it better here.

Of course, this still leaves room for an expert on the modern Russian Federation to talk about the narrative’s revival.