The greatest military blunders in history include Varus marching three legions into the Teutoburg Forest in AD 9, Napoleon's invasion of Russia in 1812, the Charge of the Light Brigade in 1854, the unfortified British camp at Isandlwana in 1879 and the Arnhem drop of 1944. What they share is not bad luck but a decision, taken despite warnings or alternatives, that turned a hard situation into a disaster.
A blunder is not the same thing as a defeat. Armies lose to better enemies, to weather and to plain chance all the time. This list covers battles where historians broadly agree that a commander's own choice did most of the damage. For the battles with the highest death tolls, see our guide to the deadliest battles in history; this one is about how armies beat themselves.
Hindsight is cheap, and several of these commanders were brave men badly served by others. But each decision below was questioned at the time or soon after, and each one cost thousands of lives.
1. Cannae, 216 BC: the army that was too deep
In 216 BC Rome put into the field the largest army in its history, around 80,000 infantry and 6,000 cavalry1, to crush Hannibal in Apulia. The plan was to win by mass: the Roman maniples were drawn up deeper and narrower than usual1 so that the infantry could punch through the Carthaginian centre. That was exactly what Hannibal invited. His centre gave ground, his African veterans closed on the Roman flanks, and his cavalry swung round to seal the rear. Packed so tightly that many men could not use their weapons, the legions were surrounded and cut down. Ancient writers put the Roman dead at 50,000 to 70,000. Some historians, Goldsworthy among them, argue that the Roman plan was reasonable on paper and failed because Hannibal read it perfectly. Even so, the deployment turned the army's size into a trap.
2. Teutoburg Forest, AD 9: the march into a trap
Publius Quinctilius Varus, governor of the new Roman lands east of the Rhine, trusted Arminius, a Cheruscan noble who held Roman citizenship and led auxiliary troops, and according to the Roman historians he dismissed a warning from another chieftain, Segestes2, that Arminius was plotting against him. In the autumn of AD 9, answering a reported revolt, Varus led three legions, the 17th, 18th and 19th2, with a long baggage train into wooded, boggy country. Over several days the strung-out column was attacked again and again until it ceased to exist.
3. Manzikert, 1071: an army divided before the battle
Before the emperor Romanos IV Diogenes met the Seljuk sultan Alp Arslan he sent a large part of his army away to besiege Khliat, and those troops never rejoined him. On the day of battle, 26 August 1071, the Byzantines advanced into a screen of Seljuk horse archers. When Romanos turned for camp at dusk, the rearguard under Andronikos Doukas, a member of a rival family, left the field instead of covering him, and the emperor was surrounded and captured. The defeat was survivable; the civil war that followed opened Anatolia to Turkish settlement.
4. Hattin, 1187: leaving the water
In July 1187 Saladin besieged Tiberias to draw out the army of the Kingdom of Jerusalem, camped by the springs of Sephoria. Raymond of Tripoli, whose own wife was inside Tiberias, reportedly advised King Guy of Lusignan to stay by the water, but Guy marched across dry country in midsummer. Saladin's horsemen harassed the column all day, the Franks camped for the night without water, and on 4 July, exhausted and surrounded on the Horns of Hattin, their army was destroyed. Guy was captured along with the relic of the True Cross. Jerusalem fell within months.
5. Russia, 1812: the campaign with no exit
Napoleon crossed the Niemen in June 1812 with the largest army Europe had ever seen, often put at around 600,000 men3 including later reinforcements, counting on a quick, decisive battle. The Russians withdrew instead. The army bled men to heat, disease and desertion, and when Napoleon reached Moscow in September the city was largely empty and soon in flames. He waited there for peace offers that never came3 and only left in October, so the retreat ran straight into the Russian winter. Estimates vary, but only a small fraction of the men who marched in came back as a fighting force.
6. The Charge of the Light Brigade, 1854: the garbled order
At Balaclava on 25 October 1854 the British commander, Lord Raglan, saw Russians hauling captured guns away from redoubts on the heights and sent a written order for the cavalry to advance rapidly and stop them. It was carried by Captain Louis Nolan to Lord Lucan4, who from the valley floor could not see the guns Raglan meant. Nolan's gesture seemed to point down the North Valley, at the main Russian battery, and Lucan passed the order to Lord Cardigan, his brother-in-law. Roughly 670 riders charged down the valley4 under fire from three sides. They reached the guns, but the brigade was wrecked within minutes.
7. Little Bighorn, 1876: dividing in front of an unknown enemy
On 25 June 1876 Lieutenant Colonel George Armstrong Custer found a large Lakota, Northern Cheyenne and Arapaho village on the Little Bighorn and attacked at once. He split the 7th Cavalry, sending three companies under Captain Frederick Benteen to scout, three under Major Marcus Reno to strike the village, and keeping five companies, about 210 men5, for himself. The village was far larger than he understood: modern historians estimate around 8,000 people with 1,500 to 1,800 warriors5. Reno was driven back, Benteen joined him on the bluffs, and Custer's own command was destroyed to the last man.
8. Isandlwana, 1879: the camp that was never fortified
On 22 January 1879, acting on reports of Zulu forces nearby, Lord Chelmsford led part of his column out of the camp beneath Isandlwana to find them. The camp had not been entrenched, and the wagons had not been drawn into a laager6. While Chelmsford searched in the wrong place, more than 20,000 Zulu warriors fell on the roughly 1,700 men he had left behind6. The firing line, stretched far from the tents, was outflanked, and most of the defenders were killed. The old story that jammed ammunition boxes doomed them is now widely doubted.
9. Gallipoli, 1915: warning the enemy first
The Allied plan of 1915 was to force the Dardanelles, knock the Ottoman Empire out of the war and open a sea route to Russia. The navy tried alone first, and on 18 March three Allied battleships were sunk by mines7 and the fleet drew back. That warned the Ottomans, and by the time troops landed on 25 April the defences had been strengthened. At Anzac Cove and Cape Helles the attackers were pinned on narrow beachheads below the heights. The campaign became a trench deadlock and was abandoned in January 1916 with the evacuation of the peninsula.
10. Arnhem, 1944: a bridge too far
Operation Market Garden, launched on 17 September 1944, was Montgomery's plan to lay a carpet of airborne troops along a road of Dutch bridges for an armoured corps to drive along. At the far end, the British 1st Airborne Division was dropped on heathland several miles from the Arnhem road bridge because planners feared flak closer to the town, so surprise was gone before the men arrived. Only one battalion, under Lieutenant Colonel John Frost, reached the bridge. Reports of SS panzer units near Arnhem were discounted, and the ground advance fell behind schedule. The Polish paratroopers of Stanisław Sosabowski, who had doubted the plan from the start, were dropped late and on the far bank of the river. Of the roughly 10,000 men who fought at Arnhem, only some 2,400 were brought back across the Rhine8.
Blunder or bad luck? What we left out
Some famous disasters are missing on purpose. Lake Trasimene in 217 BC was above all a superbly laid ambush, not simply a Roman error. At Pearl Harbor, American unpreparedness was real, but the attack succeeded mainly because Japan planned its surprise so well.
The common threads are easier to see. Commanders split their forces in front of an enemy they had not found, as at Little Bighorn and Isandlwana. They ignored or explained away warnings, as at Teutoburg and Arnhem. They trusted plans that needed everything to go right, as in Russia and at Gallipoli. And they gave or received orders so vague that brave men obeyed them to destruction, as at Balaclava.