By number of combatants, the largest battles in history were fought on the Eastern Front of the Second World War: over three million men took part in the Berlin operation of 1945 and some 2.7 million at Kursk in 1943, while about three million passed through the Somme in 1916 over four and a half months. The largest battle in Europe before the First World War was Leipzig in 1813, with over half a million soldiers; only Mukden in Manchuria in 1905 rivalled it. Before gunpowder, reliable figures above about 100,000 men per side are rare.
This guide ranks battles by how many soldiers took part, not by how many died; for death tolls, see our guide to the deadliest battles in history. Size and slaughter often go together, but not always: Cannae was small by modern standards and still one of the bloodiest days ever fought.
Every figure here is an estimate, and we give ranges where historians disagree. Two problems distort any ranking. Ancient writers routinely inflated enemy armies, and many modern battles lasted for months, with men rotating through the front, which makes them closer to campaigns than to a single clash.
Battle or campaign? Why the ranking is hard
Before the twentieth century a battle usually lasted one to three days, on ground a rider could cross in an hour. Leipzig, fought from 16 to 19 October 18131, is a battle in that classic sense. Verdun lasted ten months, and Kursk and Berlin were operations spanning whole fronts and several army groups.
Some lists go further and call Operation Barbarossa, the German invasion of the Soviet Union in June 1941, the largest battle ever, since it threw more than three million German and allied soldiers2 against the Red Army on a front from the Baltic to the Black Sea. We treat it as what it was: a campaign, the largest military operation in history, made up of many battles. The same goes for the Soviet drive to the Dnieper in the autumn of 1943, sometimes cited at close to four million men on both sides but fought as a chain of separate operations over several months.
Before gunpowder: Gaugamela, Red Cliffs and the problem of ancient numbers
Ancient historians loved big numbers. Arrian, our best source for Alexander, credits Darius III at Gaugamela in 331 BC with 1,000,000 infantry and 40,000 cavalry3, and puts Alexander's army at 7,000 cavalry and about 40,000 infantry3. No ancient state could have fed a million men on one plain, and modern estimates for the Persian army mostly fall between about 50,000 and 100,000, sometimes higher4. Even on those figures Gaugamela was one of the largest battles of antiquity.
Cannae in 216 BC is better documented: a Roman army of about 86,000 met Hannibal's roughly 50,000, perhaps 136,000 men in all, though some 10,000 Romans were left behind to guard the camps. At Red Cliffs in AD 208, the warlord Cao Cao boasted of 800,000 men5; his opponent Zhou Yu argued the real figure was far lower, and the allied armies facing him were smaller still. The war at Kurukshetra in the Mahabharata, with eighteen armies that would add up to several million warriors, is a legend preserved in an epic poem, not a battle record. In medieval Europe even the great set pieces, such as Grunwald in 1410, involved a few tens of thousands of men on each side.
The largest battle in Europe before the First World War: Leipzig, 1813
For almost a century the record belonged to the Battle of the Nations; only Mukden in Manchuria in 1905, where some 600,000 Russian and Japanese troops fought, matched it. Around Leipzig more than half a million soldiers from a dozen nations1 fought, with the allied armies of Russia, Prussia, Austria and Sweden, around 365,000 by the end, against some 195,000 under Napoleon. Estimates of the total run from about 500,000 to 600,000. Nothing else in the Napoleonic era came close: Borodino the year before involved about 250,000 men, and Waterloo fewer than 200,000. Earlier still, the relief of Vienna in 1683 set a Christian army of roughly 74,000 against an Ottoman host perhaps twice that size. Prince Józef Poniatowski's Polish corps fought on Napoleon's side, and Poniatowski, made a Marshal of France during the battle, drowned in the Elster while covering the retreat.
The First World War: battles of millions
Railways, conscription and industrial supply changed the scale completely. At the Marne in September 1914, roughly two million French, British and German soldiers fought along a front east of Paris. Verdun in 1916 drew around 1.1 million French and 1.2 million German soldiers through its sector over ten months, because both armies rotated whole divisions in and out. The Somme, from July to November 1916, drew more than three million British, Commonwealth, French and German troops through the line, and over a million of them became casualties.
For the United States, the largest battle ever fought was the Meuse-Argonne offensive, from 26 September to 11 November 1918, in which some 1.2 million American soldiers took part6; more than 26,000 of them were killed6.
The Second World War: the largest battles ever fought
The Eastern Front produced the biggest battles in history. At Moscow, from October 1941 to January 1942, around a million men or more fought on each side. At Stalingrad, roughly two million soldiers were drawn in before the German 6th Army surrendered in February 1943.
At Kursk in July 1943, Glantz and House count about 1.9 million Soviet troops against some 780,000 Germans7, with thousands of tanks on each side, in what is usually called the largest tank battle ever fought. And for the final Berlin operation, from 16 April to 2 May 1945, the Red Army and the Polish armies fighting beside it massed about two and a half million men8 against a German defence of perhaps three quarters of a million, many of them old men and boys of the Volkssturm.
Why the numbers never agree
Even for modern battles, totals depend on what is counted. Some historians include only front-line combat troops, others the full strength of the armies, with the supply, artillery and air units behind the line. Soviet and German figures were shaped by wartime secrecy and later politics, and the opening of Soviet archives after 1991 shifted many estimates. For a battle that lasted months, the number of men present on any single day can be a fraction of the number who passed through it. That is why we give ranges, and why two honest lists can rank Moscow, Stalingrad and Kursk in a different order.