Here is the summary of the worst military debacles suffered by the Romans during over 1000 years of history from the beginning of the Republic to the end of the Western Roman Empire.
In chronological order:
Battle of Heraclea (280 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Epirus & Magna Graecia[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]45,000 (8 legions + cavalry)[/TD]
[TD]35,500[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]7,500 to 15,000 killed
+ 1800 captured[/TD]
[TD]7,000 to 11,000
[/TD]
[/TR]
[/TABLE]
Battle of the Trebia (218 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Carthage[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]40,000 (4 or 5 legions + auxiliaries)[/TD]
[TD]40,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]26,000 to 32,000[/TD]
[TD]4000 to 5000[/TD]
[/TR]
[/TABLE]
Battle of Lake Trasimene (217 BCE)
Type of battle : ambush
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Carthage[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]30,000[/TD]
[TD]55,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]15,000 killed
+ 15,000 captured[/TD]
[TD]1,500 to 2,500[/TD]
[/TR]
[/TABLE]
Battle of Cannae (216 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Carthage[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]86,400 (8 legions + cavalry)[/TD]
[TD]50,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]67,500 to 85,500[/TD]
[TD]5,700[/TD]
[/TR]
[/TABLE]
Battle of Noreia (113 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Cimbri & Teutones[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]30,000[/TD]
[TD]300,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]24,000[/TD]
[TD]light[/TD]
[/TR]
[/TABLE]
Battle of Burdigalia (107 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Cimbri, Teutones, Volcae + others[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]40,000[/TD]
[TD]unknown but very large[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]10,000[/TD]
[TD]light
[/TD]
[/TR]
[/TABLE]
Battle of Arausio (105 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Cimbri & Teutones[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]120,000 (10–12 legions)[/TD]
[TD]200,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]120,000[/TD]
[TD]15,000[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Defeat caused by personal
bickering between the two
consuls, Quintus Servilius Caepio
and Gnaeus Mallius Maximus[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of Carrhae (53 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Parthian Empire[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]36,000–43,000 (7 legions + cavalry)[/TD]
[TD]10,000 cavalry[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]20,000 killed + 10,000 captured[/TD]
[TD]38 cataphracts[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Marcus Licinius Crassus killed[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of the Teutoburg Forest (9 CE)
Type of battle : ambush
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Empire[/TD]
[TD]Germanic tribes[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]16,500 to 22,500 (3 legions)[/TD]
[TD]~ 15,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]16,000 to 20,000[/TD]
[TD]minimal[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]3 legions destroyed[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of Edessa (260 CE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Rome + Germanic allies[/TD]
[TD]Sassasian Persians[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]70,000[/TD]
[TD]unknown[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]over 60,000[/TD]
[TD]minimal[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Emperor Valerian captured[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of Adrianople (378 CE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Eastern Roman Empire[/TD]
[TD]Goths & Alans[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]15,000 to 30,000 (7 legions)[/TD]
[TD]12,000 to 20,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]10,000 to 20,000[/TD]
[TD]unknown[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Emperor Valens killed[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Worst defeats by number of casualties
Note that, except for Adrianopole, none of these battles took place during the declining phase of the empire from the late 2nd century to the fall of the Western Roman Empire in 476 CE. The reason is that battles during the Late Empire were typically smaller in size. There were plenty of small battles against barbarian incursions or local rebellions, but also numerous clashes between emperors and usurpers (Emperor Gallienus had to fight at least 12 usurpers). The few major battles were usually won by Rome (such as the Battle of the Catalaunian Plains in 451 CE).
In chronological order:
Battle of Heraclea (280 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Epirus & Magna Graecia[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]45,000 (8 legions + cavalry)[/TD]
[TD]35,500[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]7,500 to 15,000 killed
+ 1800 captured[/TD]
[TD]7,000 to 11,000
[/TD]
[/TR]
[/TABLE]
Battle of the Trebia (218 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Carthage[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]40,000 (4 or 5 legions + auxiliaries)[/TD]
[TD]40,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]26,000 to 32,000[/TD]
[TD]4000 to 5000[/TD]
[/TR]
[/TABLE]
Battle of Lake Trasimene (217 BCE)
Type of battle : ambush
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Carthage[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]30,000[/TD]
[TD]55,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]15,000 killed
+ 15,000 captured[/TD]
[TD]1,500 to 2,500[/TD]
[/TR]
[/TABLE]
Battle of Cannae (216 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Carthage[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]86,400 (8 legions + cavalry)[/TD]
[TD]50,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]67,500 to 85,500[/TD]
[TD]5,700[/TD]
[/TR]
[/TABLE]
Battle of Noreia (113 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Cimbri & Teutones[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]30,000[/TD]
[TD]300,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]24,000[/TD]
[TD]light[/TD]
[/TR]
[/TABLE]
Battle of Burdigalia (107 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Cimbri, Teutones, Volcae + others[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]40,000[/TD]
[TD]unknown but very large[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]10,000[/TD]
[TD]light
[/TD]
[/TR]
[/TABLE]
Battle of Arausio (105 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Cimbri & Teutones[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]120,000 (10–12 legions)[/TD]
[TD]200,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]120,000[/TD]
[TD]15,000[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Defeat caused by personal
bickering between the two
consuls, Quintus Servilius Caepio
and Gnaeus Mallius Maximus[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of Carrhae (53 BCE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Republic[/TD]
[TD]Parthian Empire[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]36,000–43,000 (7 legions + cavalry)[/TD]
[TD]10,000 cavalry[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]20,000 killed + 10,000 captured[/TD]
[TD]38 cataphracts[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Marcus Licinius Crassus killed[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of the Teutoburg Forest (9 CE)
Type of battle : ambush
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Roman Empire[/TD]
[TD]Germanic tribes[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]16,500 to 22,500 (3 legions)[/TD]
[TD]~ 15,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]16,000 to 20,000[/TD]
[TD]minimal[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]3 legions destroyed[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of Edessa (260 CE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Rome + Germanic allies[/TD]
[TD]Sassasian Persians[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]70,000[/TD]
[TD]unknown[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]over 60,000[/TD]
[TD]minimal[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Emperor Valerian captured[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Battle of Adrianople (378 CE)
Type of battle : pitched battle
[TABLE="class: outer_border, width: 600"]
[TR]
[TD]Belligerents[/TD]
[TD]Eastern Roman Empire[/TD]
[TD]Goths & Alans[/TD]
[/TR]
[TR]
[TD]Strength[/TD]
[TD]15,000 to 30,000 (7 legions)[/TD]
[TD]12,000 to 20,000[/TD]
[/TR]
[TR]
[TD]Losses[/TD]
[TD]10,000 to 20,000[/TD]
[TD]unknown[/TD]
[/TR]
[TR]
[TD]Remarks[/TD]
[TD]Emperor Valens killed[/TD]
[TD][/TD]
[/TR]
[/TABLE]
Worst defeats by number of casualties
- Battle of Arausio (105 BCE) : 120,000 dead
- Battle of Cannae (216 BCE) : up to 85,500 dead
- Battle of Edesa (260 CE) : over 60,000 dead
- Battle of the Trebia (218 BCE) : up to 32,000 dead
- Battle of Noreia (113 BCE) : 24,000 dead
- Battle of Carrhae (53 BCE) : 20,000 dead + 10,000 captured
- Battle of Lake Trasimene (217 BCE) : 15,000 dead + 15,000 captured
- Battle of the Teutoburg Forest (9 CE) : 16,000 to 20,000 dead
- Battle of Heraclea (280 BCE) : up to 15,000 dead + 1,800 captured
- Battle of Adrianople (378 CE) : 10,000 to 20,000 dead
- Battle of Burdigalia (107 BCE) : 10,000 dead
Note that, except for Adrianopole, none of these battles took place during the declining phase of the empire from the late 2nd century to the fall of the Western Roman Empire in 476 CE. The reason is that battles during the Late Empire were typically smaller in size. There were plenty of small battles against barbarian incursions or local rebellions, but also numerous clashes between emperors and usurpers (Emperor Gallienus had to fight at least 12 usurpers). The few major battles were usually won by Rome (such as the Battle of the Catalaunian Plains in 451 CE).
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