The problem with history is, to state the obvious, that it's already happened. If you're unsure about something, there's no way to go back and check – and almost every historical period is full of gaps, uncertainties and questions that may never be answered. But sometimes historians do know the real truth, only to find that the general public has decided to go a different way, and from Julius Caesar to President Kennedy there's a whole range of historical misconceptions that are widely held – and wrong.

Click through this gallery for the most common historical myths that many people believe...

In 1963, President John F Kennedy gave one of his best-known speeches (pictured) outside the Rathaus Schoneberg in West Berlin – a direct response to the building of the Berlin Wall and the escalating tensions of the Cold War. Addressing the crowd with his usual solemn dignity, Kennedy ingratiated himself by declaring, in German, "Ich bin ein Berliner" – "I am a Berliner". At which point, the story goes, the crowd tittered, because Kennedy’s language skills did not match his statecraft. He had not said "I am a Berliner". He had said "I am a jelly donut".

We wish it were true – we really do – but this fun little anecdote is based on a false premise. A Berliner is indeed a type of donut-esque pastry, but the story rests on the idea that Kennedy’s inclusion of the article 'ein' changed the statement’s meaning (pictured here are his phonetic speech notes). The problem is that it just... doesn’t. That is not how the German language works. The word ‘Berliner’ – the donut, that is – was also not in general use in Berlin at that time. Ah well, it was fun while it lasted.

Some political propaganda is so effective that people still believe it 200 years on. It was influential British cartoonist James Gillray who caricatured Napoleon as a short, belligerent, pompous and ridiculous figure, prone to childish temper tantrums. ‘Little Boney’ actually measured five feet and seven inches (1.68m) – slightly above average for his era – but the image stuck. Napoleon himself saw and despised the cartoons, and was quoted in his later years as saying that Gillray "did more than all the armies of Europe to bring me down".

While we’re busting Napoleonic myths, he also did not shoot the nose off the Great Sphinx while in Egypt, and did not spend the night alone in the Great Pyramid. The recent Ridley Scott film Napoleon did little to dispel his many mythologies. "He came from nothing, he conquered everything", declared the movie poster, above Joaquin Phoenix’s piercing gaze. He came from a family of minor Corsican nobility, and he conquered around 2% of the known world.

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Today, the white-marble constructions of the classical world represent a popular and particular aesthetic. Neoclassical buildings like London’s Buckingham Palace, the Prado Museum in Madrid and the US Capitol gleam white-hot in the summer sun, while the elegant statues of the Renaissance favoured form over colour – in supposed homage to their Greek and Roman forebears. White marble remains a status symbol thanks to its classical connotations: grand yet graceful, opulent yet austere.

It's all rather ironic, because the great works of the classical canon were originally brightly coloured – perhaps too brightly coloured for many modern tastes. Vibrant shades abounded even on stern busts of Roman emperors and the intricate friezes of the Parthenon. Fast-forward two millennia and the paintwork has long since faded, giving rise to a range of colourless copycats that would have left the Romans cold. Here we see the famous Augustus of Prima Porta statue depicting Rome's first emperor, alongside a replica with rich red robes and patterning.

Between the surrender of France in 1940 and Germany’s invasion of the Soviet Union in 1941, Britain technically stood alone against the Nazis – but the word 'alone' is so misleading it might as well be false. At that time the British Empire covered nearly a quarter of the globe, and a mixture of carrot and stick saw men and munitions pour in from Canada, Australia, South Africa, New Zealand and beyond. India mobilised two and half million soldiers, the largest volunteer army ever assembled, while a thousand men from the Cayman Islands joined the Royal Navy – equivalent to roughly two thirds of the adult male population.

With Nazi strategists readying invasion plans and the Luftwaffe raining fire on London, the British people must have felt very isolated. Winston Churchill’s wartime speeches certainly drew on this spirit of gutsy defiance – "we shall defend our island, whatever the cost may be" – and for a few months the situation looked grim. But the popular image of Britain as a plucky David standing alone against the Nazi Goliath was never accurate – even in its darkest hours.

A stalwart of HBO shows and children’s birthday parties, the horned Viking helmet is at once both instantly recognisable and utterly mystifying. Once you know that Vikings didn’t wear them – and they didn’t, the trope emerged in the 19th century – it’s hard to understand why they ever would. Horns serve no purpose in combat besides weighing down the wearer and sometimes getting caught in trees, and would have posed a needless challenge for 8th to 10th-century blacksmiths. Only two intact Viking helmets have ever been found (pictured), and both are conspicuously smooth-sided.

Away from headwear, some Viking stereotypes are gratifyingly accurate. They did indeed travel in wooden longboats with lines of oarsmen assisted by a single sail. They did indeed wield round wooden shields and fearsome battle axes (swords were the preserve of the upper classes). And they did indeed pillage settlements across Europe with a targeted savagery that inspired fear everywhere from Asia Minor to Ireland. But they did not drink from the skulls of their enemies (because ew), and nor did they boast a class of frenzied berserker warriors who charged into battle without any clothes.

Poor Marie Antoinette. As if being publicly beheaded wasn’t bad enough, she’s now gone down in history as a byword for greed, callousness and excess, thanks mostly to a line of dialogue that is, at best, a mistranslation. The notorious phrase reads "Qu’ils mangent de la brioche", and while brioche bread was considered a luxury in 18th-century France, it’s hardly the Victoria sponge so often imagined by modern minds. More importantly – she never said it. The phrase is drawn from Confessions, a work by philosopher Jean-Jacques Rousseau which was written 24 years before the French Revolution when Antoinette was 11 years old.

Antoinette was viscerally hated in her era, but modern historians take a kindlier tone. She was a convenient lightning rod for French frustration – foreign, female, royal – even though her unhappy marriage left her with minimal power. Salacious pamphlets libelled her with cruel innuendo, and depicted her as a scheming behind-the-scenes manipulator. But, references to baked goods aside, her reputation for extravagance was well-earned. She once had an entire farm built in the grounds of Versailles so that she and her attendants could play at being milkmaids. Pictured is Kirsten Dunst in the 2006 film Marie Antoinette.

Medieval societies did think some pretty eyebrow-raising things. Widespread beliefs included that evil spirits lived inside Brussels sprouts, that cats were vessels for Satan and that rubbing yourself with a live chicken could cure plague. But 'flat Earth theory' – still occasionally believed today – was old hat even before the beginning of the Dark Ages. Ancient Greek mathematician Pythagoras was the first to argue that the world was round in around 500 BC, with fellow countryman Aristotle confirming his findings 150 years later. Fast-forward another century and Greek astronomer Eratosthenes had measured Earth's circumference – and got it right within a few miles.

We don't know what Fred the feudal farmer thought about the shape of the Earth, but, in the words of historian Jeffrey Burton Russell, "no educated person in the history of Western civilisation from the 3rd century BC onwards believed that the Earth was flat". Pictured here is a replica of the Erdapfel – the oldest surviving globe constructed by Martin Behaim in 1492. Fittingly, that's the same year Columbus sailed for America, and perhaps the most prevailing part of this myth is that he'd set out to prove the Earth was round. It's true that Columbus was trying to reach East Asia, but he was solely seeking a new trade route.

Even by the standards of medieval warfare, sieges were brutal affairs. Attackers would bombard ramparts with complex siege engines like trebuchets and ballistae, tunnel beneath fortifications to undermine their foundations, and set up perimeters to starve out garrisons over months or even years. Defenders would fire crossbow bolts through arrowslits, dig ditches to hamper ladders and siege towers, and construct tunnels of their own to maintain their crucial water supply. There aren’t many things that didn’t happen during medieval sieges, but pouring boiling oil from the battlements – a Hollywood favourite – was exceedingly rare.

Oil was valuable, difficult to use and usually in short supply, so it would have been an expensive and cumbersome addition to a fortress’s arsenal. As a general rule, ancient and medieval warfare was a lot less elaborate than pop culture would have you believe, particularly during sieges when resources were scarce. Why bother raiding your depleted kitchens for cooking oil when you could simply scald your enemy with boiling water, or, better still, clonk them on the head with a rock?

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Two heavily armed fighters locked in a single battle before a crowd baying for blood – it can be hard to see how gladiatorial combat wouldn’t end in death. But the life of a gladiator was not always nasty, brutish and short. Too much death was bad for business: if you were going to put on a good show you needed fighters that were well-trained and well-equipped, and a high fatality rate meant a poor return for promoters and investors. Gladiators may have fought to wound rather than kill, and the fate of defeated fighters was left up to the crowds. A successful gladiator could become a celebrity – with portraits in public places and even product endorsements.

Some modern estimates suggest that only one in 10 gladiatorial contests ended with death, and enough victories in the arena could earn an enslaved gladiator his freedom – symbolised by the bestowing of a wooden sword. It was Roman author Juvenal who famously wrote that "bread and circuses" were the only things necessary to keep the common people from revolt. And it’s hard to maintain a steady supply of circuses if you keep killing all the clowns.

Called 'a teardrop on the cheek of time' by Indian poet Rabindranath Tagore, the Taj Mahal is world-renowned for the transcendent beauty not only of its architecture, but its backstory. Built by heartbroken Mughal emperor Shah Jahan as a mausoleum for his beloved wife Mumtaz Mahal, the Taj is a symbol of enduring love and beauty that was always intended to ring down the centuries. So determined was he that no future monument should ever rival its beauty that Shah Jahan cut off the hands of each of the 20,000 labourers that worked on the site.

It’s easy to see why this mix of high romance and unspeakable cruelty appeals to storytellers, but it is just that – a story. Unfortunately, mass mutilations do appear elsewhere in the historical record. In the 13th century, some Mongol conquerors kept track of their victims by severing their right ears, and then counting them up in large piles. Byzantine emperor Basil the Bulgar-Slayer (pictured), meanwhile, is thought to have blinded up to 15,000 Bulgarian prisoners in AD 1014, leaving just one man in every hundred with his sight so he could lead the others home.

History is written by the winners, and perhaps nowhere is this truer than 16th-century Mexico. The Spanish conquest of the Aztecs is prime myth-making territory, as most of our sources are self-aggrandising retrospectives by victorious conquistadors describing events that happened deep in the jungle. A profound sense of cultural and religious superiority oozes from these accounts, obscuring the customs and perspectives of the defeated Aztecs, many of whom did not live to tell their tales.

Chief among these myths is the idea that the Aztecs thought the Spanish were deities – specifically the prophesied return of the creator god Quetzalcoatl (pictured). This notion was cooked up by Franciscan friars in the late-1500s, and is absent even from most Spanish sources. Even Cortes himself – the leader of the conquistadors, and one of history’s least modest individuals – makes no mention of it.

It’s comforting to think that misunderstood genius might lie dormant within us all, and the claim that Einstein failed maths as a child has provided solace to generations of underachieving schoolkids. There’s a grain of truth here – in 1895 Einstein took and failed an entrance exam to study electrical engineering in Zurich aged 16 – but he always excelled at maths and science and had taught himself geometry by the time he turned 12. He earned a PhD in 1905 – the same year he published his paper on the special theory of relativity.

This myth began to circulate in newspapers as far back as the 1930s, so Einstein (pictured, left) had the pleasure of personally dispelling it. "Before I was 15 I had mastered differential and integral calculus," he quipped. We’re not claiming the education system always gets the best out of promising pupils, but if you failed maths at school the Nobel Prize for physics will likely continue to elude you.

Julius Caesar is one of history’s main characters – a military and political leader with an astonishing sense of his own innate destiny. Shakespeare wrote that he sat “bestride the narrow world like a Colossus”, and he certainly did some pretty imperial things. He subjugated Gaul (France) with a ruthlessness that has been compared to genocide, quite literally changed time by instituting the 365-day calendar, and was brutally assassinated by Roman elites on the steps of the Senate – classic emperor behaviour. But although a Caesar was Rome’s first emperor – it wasn’t Julius.

Julius Caesar oversaw the dying days of the Roman Republic – a democracy spearheaded by two elected consuls who were limited to one-year terms. Caesar became consul in 59 BC, and used a mix of military victories and backroom deals to accumulate a frightening amount of power. In 44 BC he was declared ‘dictator for life’ and was promptly murdered by a group of senators, whose own ambitions aligned with concerns that Caesar wished to make himself king. It was Augustus Caesar – Julius’s great-nephew and adopted son – who emerged victorious from the civil wars that followed, and installed himself as the first emperor of an exhausted Roman state.

The iron maiden has entered folklore as one of the cruellest methods of torture to emerge from the Middle Ages – and that’s a crowded field. An upright casket akin to a sarcophagus adorned with rows of inward-facing spikes, one can only imagine the horrors that awaited its victims in windowless medieval torture chambers. But imagining is all we can do, as the iron maiden is a late-18th-century fabrication – a myth concocted to make the Dark Ages seem even darker. The first iron maidens were in fact cobbled together in the 19th century and passed off as historic artefacts in museums.

We’re quite relieved that no poor prisoner had to end their days becoming a spike sandwich in an airless metal box. But for the more morbid among you, there are plenty of real torture methods that were meted out liberally in medieval dungeons. The rack was a torture chamber staple, and stretched out victims until their joints dislocated, often leaving them unable to walk. So too were thumbscrews, vicious little metal contraptions that would crush a person’s fingers and thumbs.

Perhaps the final boss of all history myths, this misconception is so ingrained that the United States has an entire federal holiday celebrating it. In 1492, Columbus sailed the ocean blue and made landfall in the Bahamas on behalf of the Spanish crown. He never actually set foot on the North American continent, but Viking explorer Leif Erikson did nearly 500 years previously, with his landing in modern-day Canada recorded in the semi-mythical Vinland sagas. In the 1960s this legend was confirmed by the discovery of L’Anse aux Meadows, a ruined Viking settlement on the Newfoundland coast.

If you want to go back even further, the first people to discover America were early humans from Asia, who reached North America by land when the continents were still connected and from whom all Native Americans are descended. Columbus (pictured) was certainly important – his voyages kicked off the rapid colonisation of the New World – but even he didn’t think he’d discovered America. He’d set out to find an alternative route to East Asia, and maintained until his dying breath that that’s what he’d done.

Read on to discover the most common misconceptions about the history of the US