THE AMERICAN CIVIL was entering its 18th month in September of 1862 when two colossal armies met 60 miles northwest of Washington D.C. in a quiet corner of Maryland

On Sept. 13, 1862, 55,000 Rebel troops under the command of Robert E. Lee invaded the neutral border state in hopes that the presence of a large Southern army would compel residents there to join the rebellion.

More than 75,000 Union troops under the command of George McClellan intercepted the Confederates and forced a decisive clash just outside town of Sharpsburg near a small stream called Antietam Creek.

Hostilities began at dawn on Sept. 17 and continued into the late afternoon. The opposing armies fought each other to a standstill before the guns fell silent at around 6 p.m. By the time the action was over, more than 20,000 men had become casualties; nearly 4,000 of them would breathe no more.

While far costlier clashes would follow over the next two-and-a-half years of war, to this day the Battle of Antietam remains the bloodiest single-day in all of American history — worse than both Pearl Harbor and 9/11.

Sadly, other nations’ armies have known far deadlier one-day battles. Consider these:

Britain lost nearly as many men in the first hours of the four-month bloodbath known as the Somme Offensive than were killed in any of England’s wars of the previous 100 years. On July 1, 1916, more than 54,000 Tommies from the Third and Fourth armies were shredded by machine gun and artillery fire as they trudged slowly across No Man’s Land towards the German lines just east of the town of Albért. The assault left 20,000 dead. Within minutes of going over the top, whole units were virtually annihilated. Some outfits, like the Royal Newfoundland Regiment, suffered losses in excess of 90 percent. Although Anglo-French forces did manage to overrun the German trenches at a number of points along the 20-kilometre (12-mile) front, the Allied effort soon bogged down, ushering in a deadly 141-day stalemate that created more than a million casualties. For many, the slaughter on the Somme remains a powerful symbol of the high human cost of trench warfare.

As terrible as it was, July 1, 1916 wasn’t the deadliest day in British history. An even bloodier one occurred more than 450 years earlier in Yorkshire during the War of the Roses. On Palm Sunday, March 29, 1461, 30,000 of King Edward IV’s soldiers met a 35,000-man army loyal to the House of Lancaster near the small town of Towton. The two factions clashed all day while a freak springtime blizzard blew around them. Contemporary chroniclers estimated that by the time the killing had subsided, 27,000 Englishmen had been hacked to death — roughly 1 per cent of the population of the entire country at the time. [1] In recent years, some historians have revised the body count to fewer than 10,000, but others still maintain the original death toll. [2]

There is no ambiguity over how many French soldiers perished at Rossignol near the Ardennes on Aug. 22, 1914. In a desperate bid to stem the German advance into France during what is now known as the Battle of the Frontiers, more than 27,000 soldiers of the Third Republic were mowed by the Kaiser’s army in a day. It remains the bloodiest 24 hours in France’s history.

June 18, 1815 was another dark day for France. That’s when Napoleon’s Grande Armée was bloodied at Waterloo following the exiled emperor’s ill-fated return to power. Up to a third of Bonaparte’s men (25,000 in all) became casualties in the ten-and-a-half-hour showdown, although it’s unclear exactly how many were actually killed. British losses are estimated at about 15,000 dead and wounded, while the Prussians took 7,000 casualties. All told, as many as 30,000 lay dead before nightfall. While surveying the devastation, the victorious Duke of Wellington famously summed up the day: “Nothing except a battle lost can be half as melancholy as a battle won.” It’s been said that the dead were so plentiful, local scavengers made fortunes selling teeth pulled from the mouths of the corpses that littered the filed. Dentists bought up the grim trophies by the thousand and supposedly used them in the manufacturer of false teeth for years to come. In fact, for a generation after the epic slaughter, dentures throughout Western Europe were known as “Waterloo teeth.”

Fresh from a costly victory at Thermopylae in 480 BCE, the Persian emperor Xerxes I was just days away from another epic thrashing. In a bid to subdue the whole of Greece, the conquering monarch planned to use 900 galleys to sail his army around Attica and land on the Isthmus of Corinth, thus driving a wedge between the Hellenic city-states. Hoping to strike a crippling blow against the invaders, the statesman-general Themistocles gathered a flotilla of boats and waited for the unwieldy Persian fleet to sail into a cramped two-mile-wide channel between the island of Salamis and the mainland. When the moment was right, the Athenian general struck with a vengeance. Despite being outnumbered more than three-to-one, the Greek ships rowed into the midst of the Persians using their rams to smash the hulls of the enemy craft. Heavily armed hoplites leapt onto the crippled boats putting to the sword all that they could. Xerxes’ own brother, the admiral Ariabignes, was among the first to fall. As the slaughter continued, panic gripped the Persian fleet. Xerxes’ ships veered away from the Greeks and collided with one another. Some vessels ran aground; others capsized sending their 150-man crews toppling into the choppy waters. According to the ancient historian Herodotus, many of the Persians couldn’t swim while others, weighed down by their armour, sank straight to the bottom. Within minutes, up to 300 Persian vessels were swamped and as many as 40,000 of the invaders had drowned. Xerxes himself watched horrified from shore as the entire debacle unfolded.

The Roman Republic suffered an even more humiliating defeat than the Persians – and this one only a few days’ march from the Eternal City itself. On Aug. 2, 216 BCE, a 50,000-man army under the Carthaginian generalissimo Hannibal surrounded and butchered a force of nearly 90,000 Italian soldiers led by Gaius Terentius Varro at Cannae. Despite outnumbering the invaders by a wide margin, the heavily armoured Roman spearmen were no match for the faster-moving Carthaginian infantry. Hannibal’s army quickly outflanked and enveloped the Romans and within hours had hacked them to pieces. According to contemporary estimates, more than 50,000 Romans were slain in the melee — roughly 20 per cent of Rome’s military-aged male population. [3] Following the slaughter, Hannibal collected the rings from the dead and sent them home where they were dramatically heaped upon the steps of the Punic assembly. With the Carthaginians poised to sack Rome itself, hysteria and despair gripped the population. In a desperate bid to stave off defeat, panic-stricken Roman citizens even resorted to human sacrifice to curry the favour of the gods. The senate quickly cobbled together a replacement army and sent it into the field to halt the enemy advance. Hannibal dispatched emissaries to negotiate a truce, but the Republic remained defiant. In fact, city authorities outlawed the use of the word “peace” for a time. [4] Local resistance soon stiffened and Hannibal abandoned the campaign and returned his weary army to North Africa.

The deadliest one-day battle in all of history was fought on Russian soil at Borodino in the late summer of 1812. Just three months earlier, Napoleon had invaded Tsar Alexander I’s empire with what was heralded at the time as the largest army ever assembled: 680,000 men. All summer, the French ruler had marched his sprawling legion across the dusty plains of Russia straight towards Moscow. But as the campaign progressed, a series of battles coupled with a typhus epidemic halved Bonaparte’s army. By September, nearly 150,000 Russian soldiers gathered to block the French at Borodino — about 120 km (80 miles) due west of the country’s historic capital. The fight kicked off shortly after dawn on Sept. 7 and kept raging all day. By sunset, the Russian army was in tatters — as many as 45,000 of the Tsar’s troops were either wounded or dead. French casualties were slightly lower, but still shocking: 35,000 killed and injured, including 49 generals. Bloodied but triumphant, Napoleon pushed on to Moscow. Within a week, his standard was waving over St. Basil’s Cathedral. Unfortunately for the conquerors, saboteurs set fire to the city. With his army in control of a smouldering ruin, winter coming and fresh Russian reinforcements massing to the south, Napoleon impulsively ordered his army to give up their prize and march for home. Sub-zero temperatures and marauding Cossacks soon made their two-month retreat a living hell. Out of the original invasion army, fewer than 100,000 French and allied troops made it out of Russia alive.