Imperial Rome's legions and Genghis Khan's Mongol horde are two of the most successful war machines in history, separated by a thousand years. One side is disciplined heavy infantry backed by the best engineering of the ancient world. The other is a nation of mounted archers who conquered more land than anyone before or since. So who wins on a single battlefield?
The Roman Legions: Who They Were
For this matchup we take the Roman army at its peak, in the late 1st and 2nd centuries AD under emperors like Trajan and Hadrian. A legion had roughly 5,000 professional heavy infantrymen who had signed up for 25 years of service. They trained constantly, marched up to 30 kilometres a day in full kit, and built a fortified camp every single night on campaign.
Legions rarely fought alone. Each was supported by roughly the same number of auxilia, non-citizen troops who supplied what the legion lacked: cavalry, archers from Syria and Crete, and slingers from the Balearic Islands. Rome's real strength was organisation. Supply depots, roads, engineers and a command structure that could replace a fallen officer on the spot let Rome keep armies in the field for years.
The Mongols: Who They Were
The Mongol army of the 13th century was built around the horse. Every man was a rider who had learned to shoot from the saddle as a child. Genghis Khan organised them in a strict decimal system: units of 10, 100, 1,000 and the 10,000-strong tumen. Loyalty went to the unit and the Khan, not to a tribe, which ended centuries of steppe infighting.
Each warrior brought several spare horses, often three to five, so a Mongol army could cover distances that looked impossible to its enemies. Scouts ranged far ahead, messengers used a relay system called the yam, and generals such as Subutai coordinated separate columns across hundreds of kilometres.
Weapons and Armour
- Romans: the large curved scutum shield, the gladius short sword for close work, two pila (heavy javelins designed to bend and pin enemy shields), and segmented plate or mail armour with an iron helmet. Artillery such as the bolt-throwing scorpio could be carried into the field.
- Mongols: the composite recurve bow of horn, wood and sinew, powerful enough to kill at well over 100 metres, with different arrows for armour, horses and long range. Light cavalry wore leather or padded armour. Heavy cavalry wore lamellar armour and carried lances, sabres and maces for the final charge.
Tactics and Leadership
Roman tactics depended on closing with the enemy. Legionaries threw their pila, then pushed forward shoulder to shoulder, with fresh lines rotating to the front. Against infantry armies this was almost unbeatable.
The Mongols simply refused to be caught. Horse archers rode up, shot, and wheeled away. The favourite trick was the feigned retreat: pretend to flee, draw the enemy out of formation, then turn and destroy the scattered pursuers with heavy cavalry. At Mohi and Legnica in 1241, Mongol armies used exactly these tactics to shatter the best armoured knights of Hungary and Poland within days of each other.
A History Lesson Rome Already Learned
Rome actually faced something similar. In 53 BC the Roman general Crassus marched about 40,000 men into Mesopotamia against the Parthians. At Carrhae, Parthian horse archers, resupplied with arrows by a camel train, shot the Roman formation to pieces while armoured cataphracts punished any unit that broke out. Around 20,000 Romans died and 10,000 were captured.
But Rome adapted. In 39 and 38 BC, Publius Ventidius Bassus beat Parthian armies by choosing hilly ground, fortifying positions and using massed slingers who outranged the archers. Two centuries later, the governor Arrian wrote a battle plan against the horse-riding Alans. It combined a deep infantry block with archers and artillery behind it. Rome could fight horse archers, but only when it chose the ground.
How the Battle Would Play Out
Imagine two legions with their auxilia, about 20,000 men, against two Mongol tumens of similar size on open plains.
The Mongols would find the Romans days before the Romans found them. They would harass the column on the march, pick off foragers and cavalry, and cut supply lines. When the Romans finally formed for battle, the Mongols would not attack the shield wall head on. Arrows would fall for hours. The scutum and armour would stop many of them, but horses, auxiliaries and anyone on the flanks would suffer. Roman cavalry would be baited into a pursuit and ambushed.
The Romans' best hope would be to dig in. A fortified camp on high ground, with slingers, archers and scorpios on the walls, could hold out and inflict serious losses. The Mongols were also excellent at sieges, using Chinese and Persian engineers, but a mobile field army would not have them on hand.
Verdict: Who Wins?
On open ground, the Mongols win. Speed, range and patience beat heavy infantry that cannot catch its enemy, exactly as Carrhae showed. Rome's advantages of discipline, engineering and logistics make it very hard to destroy, and in hills, forests or behind fortifications the legions could turn the fight into a grinding stalemate that favours them.
The community agrees, with the Mongols currently leading the vote. Do you think Roman adaptability could close the gap? Cast your vote on the homepage.
Sources and Further Reading
- Plutarch, Life of Crassus (account of Carrhae)
- Arrian, Ektaxis kata Alanon (Order of Battle against the Alans)
- Adrian Goldsworthy, The Complete Roman Army
- Timothy May, The Mongol Art of War
- Jack Weatherford, Genghis Khan and the Making of the Modern World