How big was the Mongol Empire next to Rome and Britain?
TL;DR — By Rein Taagepera’s estimates the Mongol Empire reached about 24 million km² around 1300, more than five times Rome’s 4.4 million; only Britain’s empire later grew larger.
The Mongol Empire was larger than any state before it, and about five times the size of Rome. Rein Taagepera of the University of California, Irvine, who measured the areas of empires from 3000 BC onward, put the Mongol Empire at 24 million square kilometers at its peak, around 1300, and Rome at 4.4 million in the centuries when it was the largest state on Earth. David O. Morgan, in the Encyclopaedia Iranica, calls it “the most extensive land empire known to history.”
Quick facts
- When
- Peak around 1300 (Taagepera dates it to about 1309); split into four khanates about 1260–1262
- Where
- From China and Korea to the south Russian steppe, Iran and Iraq; Mongol troops reached Hungary in 1241
- Who
- Genghis Khan and his successors; Rein Taagepera of the University of California, Irvine, who measured empire sizes
- Outcome
- About 24 million square kilometers, larger than any state before it; only the British Empire, at 34 to 35 million in the 1920s, grew larger
Measuring empires in megameters
Taagepera needed a unit large enough for empires. “As an area unit of convenient size, megameters squared (Mm2) were chosen,” he wrote in 1978. “Since 1 Mm = 1000 km, we have 1 Mm2 = 10^6 km2 = 386,000 square miles.” One Mm² is a million square kilometers.
His table of the largest state at each half-century shows the Mongols’ growth. The Jurchen Jin state of northern China leads in 1200 with 2.3 Mm². The Mongols take first place by 1250 with 18 Mm² and reach 24 Mm² in 1300. By 1350 the largest state is the Yuan, the Mongol dynasty in China, at 11 Mm². In his list of the 20 largest states that ever existed, the Mongol Empire stands second, at 24 Mm², with a peak date of about 1309.
Where Rome fits
In the column for the largest state, Rome appears only at AD 250, 300 and 350, at 4.4 Mm² each time. Taagepera remarked on it: “It may come as a shock, for instance, that Rome hardly appears on the world’s largest empire curve: It only makes it for about 200 years, after the disintegration of the Chinese Han empire.” The Han, in his figures, covered 6.5 Mm² in AD 100.
Rome is missing from his list of the 20 largest states of all time, whose last entry, the Tang empire of China, covered 5.2 Mm². Taagepera asked whether “our Europocentric world view has boosted Rome’s importance excessively.”
Britain and the larger total
One empire did pass the Mongols. In a 1997 paper Taagepera wrote that “Russia never surpassed the Mongol empire in size, while Britain did,” by “a considerable margin (35 Mm2 versus 24),” and he dated the British peak, 35 Mm², to 1925. His 1978 list ranks the British Empire first, at 34 Mm² around 1920.
The Mongol record is for land in one unbroken stretch. Columbia University’s Asia for Educators describes the Mongol realm as “the largest contiguous land empire in world history.”
From one realm to four khanates
The empire reached Europe early and held together only briefly. “By 1241, Mongol troops had reached all the way to Hungary,” Asia for Educators records, “but had to withdraw that very year because of the death of Ögödei, the Great Khan.” Across the realm, OpenStax notes, relay stations called yam stood “at one-day intervals from one another.”
The unity did not last. “By 1260,” according to Asia for Educators, “the Mongol domains had been split into four discrete sectors.” Peter Jackson, in the Encyclopaedia Iranica, lists them: the qaghan’s dominions in China and Mongolia, the Chaghatayid khanate in Central Asia, the Golden Horde, and the Ilkhanate in Iran and Iraq. The Mongol lines lasted unevenly: the Ilkhans ruled Iran until 1353, the Chaghatayids lasted until 1678, and the Golden Horde survived until 1502, or, through the khanate of the Crimea, until its annexation by Catherine the Great in 1783.
Key facts
- Taagepera measured empires in Mm²; one Mm² is a million square kilometers (Taagepera 1978).
- The Mongol Empire reached 24 Mm² by 1300, with a peak around 1309 (Taagepera 1978).
- Rome led the world only from AD 250 to 350, at 4.4 Mm², and is absent from Taagepera’s list of the 20 largest states (Taagepera 1978).
- The British Empire passed the Mongols, at 35 Mm² in 1925 by Taagepera’s 1997 figure and 34 Mm² around 1920 in his 1978 list.
- Mongol troops reached Hungary in 1241 and withdrew that year after Ögödei’s death (Asia for Educators).
- By about 1260 the empire had split into four khanates (Asia for Educators; Jackson).
FAQ
Was Rome the largest empire in history?
No. In Rein Taagepera's estimates Rome covered 4.4 million km² when it was the largest state on Earth, between AD 250 and 350, and it does not appear among his 20 largest states of all time.
How big was the Mongol Empire?
About 24 million square kilometers at its peak around 1300, by Taagepera's estimate, second only to the British Empire among all states he measured.
Was the British Empire bigger than the Mongol Empire?
Yes, in total area. Taagepera gives the British Empire 35 million km² in 1925, against 24 million for the Mongols. The Mongol Empire is described as the largest contiguous land empire.
How far west did the Mongols reach?
To Hungary, by 1241. They withdrew the same year after the death of the Great Khan Ögödei.
When did the Mongol Empire break up?
By about 1260–1262 it had split into four khanates: the qaghan's lands in China and Mongolia, the Chaghatayid khanate in Central Asia, the Golden Horde, and the Ilkhanate in Iran and Iraq.
Sources
- Rein Taagepera, "Size and Duration of Empires: Systematics of Size," Social Science Research 7 (1978), eScholarship, University of California
- Rein Taagepera, "Expansion and Contraction Patterns of Large Polities: Context for Russia," International Studies Quarterly 41 (1997), eScholarship, University of California
- Encyclopaedia Iranica, David O. Morgan, "ČENGĪZ KHAN"
- Encyclopaedia Iranica, Peter Jackson, "MONGOLS"
- Asia for Educators, Columbia University, "The Mongol Conquests"
- Asia for Educators, Columbia University, "How a Small Group of Mongols Conquered Such a Vast Domain"
- Asia for Educators, Columbia University, "The Collapse of the Empire"
- OpenStax, World History Volume 1, 14.2 "Chinggis Khan and the Early Mongol Empire"
Cite this article
- APA
- Song Letter. (2026, October 11). How big was the Mongol Empire next to Rome and Britain? Our Earth's History. https://ourearthshistory.com/east-asia/medieval/mongol-empire-largest-land-empire-not-rome/
- Chicago
- Song Letter. “How big was the Mongol Empire next to Rome and Britain?” Our Earth's History, October 11, 2026. https://ourearthshistory.com/east-asia/medieval/mongol-empire-largest-land-empire-not-rome/.
- MLA
- Song Letter. “How big was the Mongol Empire next to Rome and Britain?” Our Earth's History, 11 Oct. 2026, https://ourearthshistory.com/east-asia/medieval/mongol-empire-largest-land-empire-not-rome/.
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