Mavi Boncuk |The map above shows how big the Roman and Mongol Empires were at their respective peaks. The Mongols had the world’s largest contiguous land based Empire in history (and the second largest overall after the British), but just how much bigger was it than Rome?
Mongol Empire: 24 million km2 (9.27 million mi2), 17.81% of world land area in 1270 or 1309 Roman Empire: 5.0 million km2 (1.93 million mi2), 3.71% of world land area in 117 SOURCE