On the morning of 16 August 1819, an immense crowd poured into Manchester, perhaps the largest the town had ever seen. They came in an orderly and peaceful fashion. Banners bearing slogans such as “Liberty and Fraternity” and “Taxation without Representation is Unjust and Tyrannical” flapped in the breeze, and bands played patriotic tunes including Rule Britannia and God Save the King. It was a fine and sunny day.

On they came in cheerful mood; organised contingents from Bolton and Bury; 6,000 marching from Rochdale and Middleton; others from Saddleworth and Stalybridge; 200 women dressed in white from Oldham, together with families bringing their children and picnics with them.

If later estimates that 60,000 people gathered at St Peter’s Field that day are correct, it means that practically half the population of Manchester and the surrounding towns (a crowd somewhat larger than that at Manchester City home matches today) had come to attend a meeting calling for parliamentary reform. Having the vote mattered, they believed; it would change everything and force politicians to listen to their views and needs – and respond.

A young businessman, 25-year-old John Benjamin Smith, was watching with his aunt from a window overlooking the open space on the edge of the town near St Peter’s Church. He later wrote: “There were crowds of people in all directions, full of good humour, laughing and shouting and making fun … It seemed to be a gala day with the country people who were mostly dressed in their best and brought with them their wives, and when I saw boys and girls taking their father’s hand in the procession, I observed to my aunt: ‘These are the guarantees of their peaceable intentions – we need have no fears.’”

The people were expecting speeches and a good day out. What they were not anticipating was violence, carried out by troops sent in to disperse them, so aggressively that 18 people would be killed and more than 650 injured in the bloodiest political clash in British history. What happened at St Peter’s Field would become known as the Peterloo Massacre – a name coined by a local journalist named James Wroe in punning reference to the Battle of Waterloo four years earlier. Wroe paid for the joke by seeing his radical newspaper, the Manchester Observer, closed down, and was himself sentenced to a year’s imprisonment for seditious libel.

On the face of it, a Monday morning in August was a strange time to hold a political rally. Most factory workers would be at their machines – the deafening, ceaseless, clacking cotton spinning machinery that ran in the mills day and night. An industry was taking off: there were 2,400 power looms locally in 1813; 14,000 by 1820, and 115,000 within 15 years. But the handloom weavers, who worked from home and traditionally took Mondays off after working all weekend, were available. They were still in the majority in the Lancashire cotton trade: 40,000 in Manchester alone, compared with 20,000 spinning-machine operatives in the factories – but they feared for their jobs, skills, lifestyles and standards of living. Wages had halved since the end of the Napoleonic war: 12 shillings a week for 16-hour days, if you could get the work; a decade earlier, it had been 21 shillings a week.

As in many other towns during the industrial revolution, the population of Manchester was expanding rapidly: from 24,000 in 1773 to 108,000 half a century later. The Times reported from the inner-city New Cross area in the week of Peterloo: “It is occupied chiefly by spinners, weavers and Irish of the lowest description … its present situation is truly heart-rending and over-powering. The streets are confined and dirty; the houses neglected and the windows often without glass. Out of the windows the miserable rags of the family … hung up to dry; the household furniture, the bedding, the clothes of the children and the husband were seen at the pawnbroker’s.”

But not this day: they were wearing their Sunday best. Many of the crowd were literate and articulate, and where previously they had struck for better wages and petitioned the king for food, now they also wanted political change. They wanted a reformed parliamentary system in which Manchester would get representation for the first time, and a rotten borough like Old Sarum, a windswept hill outside Salisbury largely abandoned since the Middle Ages, would no longer send two MPs to Westminster.

If there was to be representation, they wanted a share in it, with working men to have a vote alongside the propertied classes. Female reform societies had also recently sprung up across the north-west, calling for votes for women. They had already been subjected to ridicule, depicted by cartoonists such as George Cruickshank as sluts and whores, abandoning their families to meddle in things they had no business to think about. That was why the women dressed in white on this day – to symbolise purity of character and motive. It was also why the cavalry would single them out for attack: if they wanted the same rights as men, they could face the same treatment.

A tapestry created by the Peterloo Memorial Campaign Group in 2017. Photograph: Christopher Thomond/The Guardian

What happened to the crowd that day has marked British politics ever since. For the Guardian, the events of that day 198 years ago have a special significance. They prompted John Edward Taylor, a 28-year-old Manchester businessman and witness to the massacre, to start his own paper, two years later, to campaign for reform. The Manchester Guardian’s roots, and its enduring liberal, reformist character, lie in what happened there in 1819.

The Peterloo massacre has become a battle honour for the left, its memory played out in a thousand mass meetings, in a direct line from August 1819 to Jeremy Corbyn’s campaign rallies today. The sight of blundering, overbearing, unreasoning authority reacting with violence to peaceful demonstrators would recur on Bloody Sunday in Derry in 1972, and at the battle of Orgreave during the miners’ strike in 1984. Each incident was followed by official denial, obstruction and manipulation in order to deflect criticism of culpability.

Other demonstrations had been put down ruthlessly before, but none in Britain had been marked with such brutality or as many deaths as Peterloo. Unlike at some other attempted rallies of that period, those attending the St Peter’s Field meeting were peaceful and law-abiding, demanding reform by constitutional means – and yet they were mown down. Their martyrdom has given them iconic status on the political left.

St Peter’s Field, a flat, three-acre open space on the edge of the town was only just big enough for the assembling masses, and did not offer much breathing space for 60,000 people. The radical activist Samuel Bamford, one of the key witnesses on the day, reported that by midday, at the centre of the field, where two carts had been roped together to form the hustings for the speakers, people were packed so close together that “their hats seemed to touch”.

The man they had come to hear was Henry Hunt, the brass-lunged orator of the parliamentary reform movement. Hunt was a tall, handsome man, from a very different background to those he was addressing. He had inherited 3,000 acres of prime land in Wiltshire when his father died, but had squandered his inheritance and eloped with a friend’s wife. It was only when he found himself ostracised by the county gentry that he became a radical. He had built a career (though not yet a parliamentary one; he would briefly become an MP in 1830) by chasing radical causes, and his fluency meant he was feared by the landed classes. “Orator” Hunt flirted rhetorically with violence – the government must be changed “peacefully if we may, forcibly if we must” – but steered well clear of inciting his audiences to rebellion.

Dressed in his trademark white top hat, Hunt was revered by working people. He was egotistical and vain, with a tendency to fall out with his followers, not always for political reasons. Hunt had been at controversial and even violent meetings before, not least at Spa Fields in central London in December 1816, when a breakaway, radical faction had started a riot in the hope of provoking a general uprising. Those plans were foiled when armed troops prevented the mob from attacking the Bank of England. Local magistrates and ministers of the Tory government plainly wished for Hunt to be arrested, but he had so far escaped imprisonment. Mass meetings he attended in London, Birmingham and Leeds in the summer of 1819 had passed off peacefully, as had a previous meeting he had addressed at St Peter’s Field that January.

Hunt claimed in his memoirs the following year that he had not wanted to be involved in the August meeting. It had originally been scheduled for 9 August, but that was cancelled following warnings by magistrates that the organisers’ intention for the meeting – to “elect” an unofficial MP to represent the people of Manchester – would be a seditious act. When Hunt arrived, he was furious to find that the meeting had been called off, but reluctantly stayed for the rearranged meeting a week later, which would only discuss parliamentary reform in general terms, and so was allowed to go ahead.

Campaigners in Manchester’s Albert Square in August 2017 carrying the names of those killed or injured at Peterloo. Photograph: Christopher Thomond/The Guardian

The memoirs give a flavour of Hunt’s vanity: “Everything conspired to impress on my mind the conviction that I alone had the power of conducting this great meeting in a peaceable, quiet and constitutional manner. I made up my mind not to desert them.”

Hunt loftily despised Joseph Johnson, one of the organisers of the Manchester meeting, for being a brush-maker. He described staying at Johnson’s house as “one of the most disagreeable seven days that I ever passed … however, most fortunately for me, Johnson was from home a considerable portion of this time, attending to his brush-making”.

Hunt presented himself to the authorities the weekend before the meeting, to check that there were no plans to arrest him. He was told no charges were planned. The meeting was legal and would go ahead.

But the authorities feared a violent outbreak, and a spark that would ignite an English revolution to follow the French. The storming of the Bastille in 1789 and the terror that followed were well within living memory. Ministers had reason to be nervous. There had been a series of uprisings and localised violence in the preceding few years, mainly about food and living conditions in the years of shortages and unemployment that followed the end of the Napoleonic wars. Luddites had broken machinery in mills across the country, attempts to stir up nationwide protests such as the abortive Pentrich revolution had been met with harsh punishment, and even peaceful protests such as an attempted march on London by unemployed weavers from Lancashire in March 1817 had been dispersed by troops.

Lord Sidmouth, then home secretary, used undercover spies to gain intelligence about subversive activities. His actions had been widely criticised, but in the absence of a civilian police force, the options were limited. If unrest was threatened, local militias, amateur yeomanry on horseback or the army had to be called out. Sidmouth had spoken in private about the country being tranquillised by bloodshed, and he guaranteed that the civic authorities could rely on parliament to indemnify them if violence did break out.

The Manchester meeting was going to be the biggest of the summer so far, and the authorities were jittery. In case of violence, they had ordered stones and rocks to be removed from the site. Manchester was still run like a small country town, by a medieval system. In times of crisis, 18 volunteer magistrates and a stipendiary full-time magistrate took charge of law and order, and it was this body of anxious men who would precipitate the crisis of the day. They were men of property – lawyers, retired businessmen and even Church of England clergymen – and not likely to be sympathetic to political reform or to the people proposing it. They believed that non-conformists and agitators were stirring up the workers to discontent. James Norris, the stipendiary magistrate, was known as a man of urbanity and gentlemanly manners, but his colleague the Rev William Hay was fiercer. “When he winks, heaven blinks, when he speaks, hell quakes,” as a local rhyme had it. The chairman of the magistrates on the day was 32-year-old William Hulton, a local landowner who was inexperienced as a law enforcer.

At their command for the meeting was Manchester’s deputy constable, Joseph Nadin, a former spinner and the town’s chief thief-taker. This corrupt, much-feared figure was responsible for carrying out any instructions given him by the magistrates that day. Described by the radical Samuel Bamford, Nadin’s manner “was rude and overbearing to equals or inferiors”. Sometimes called the real ruler of Manchester, Nadin was growing rich on bribes and kickbacks.

The town’s loyalists – Tory supporters, opposed to the radicals – have been largely written out of the Peterloo story, but they were numerous and fearful. Among them were local cotton traders and mill owners, many of whom were in favour of parliamentary reform – not to give their workers the vote, but to gain greater commercial clout for themselves. They were alarmed by the prospect of the meeting, the training of workers on the hillsides and the incendiary speeches of orator Hunt. Some had sent their families out of town.

They had their own newspapers arguing against reform and, more significantly, had already funded the creation of a local mounted militia, the Manchester Yeomanry, in 1817, specifically to guard against the mob. The troops, resplendent in dashing new blue-and-white uniforms, with peaked shako helmets and red cockades and armed with sabres, were made up of local Tory businessmen, shopkeepers, lawyers and their sons. They were spoiling for a fight, in order to show the radicals who was in charge.

The magistrates were taking no chances, and had signed up 400 special constables armed with long wooden truncheons. They also deployed 60 yeomanry troops from Manchester (with another 420 from Cheshire in reserve), called in 340 regular cavalry from the 15th Hussars, plus 400 infantry and two six-pounder cannon from the artillery. There were more than 1,500 soldiers and constables in all.

The rescheduled meeting had been widely publicised. Its modest purpose was to consider “the propriety of adopting the most LEGAL and EFFECTUAL means of obtaining a REFORM”. Nevertheless, Hunt issued a statement urging “steady, firm and temperate deportment” in those attending: “Our enemies will seek every opportunity by means of their sanguinary agents to incite a riot, that they may have a pretence for spilling our blood, reckless of the awful and certain retaliation that would ultimately fall on their heads.” They should bring “no other weapon but that of a self-approving conscience”.

It was set to be a national event, and newspapers from London and other cities sent reporters to cover it – a considerable innovation for the time; few events in British history had been reported in such detail. More than 300 people would later give accounts of what they had seen, and there were 10 press reports in the days following the meeting. John Tyas, a reporter from the Times, was on the hustings and was arrested, so a report was filed to London for him by Taylor, who would go on to found the Guardian. Jeremiah Garnett, the Guardian’s second editor, was also at Peterloo, working for the loyalist Manchester Courier, but it refused to print his report and he left the paper. In the months ahead, the authorities’ side would depend heavily on the testimony of a few troops and loyalists to contradict the weight of evidence against them. The clash of evidence from many disinterested observers, including respectable businessmen and clergy on the one side, versus many fewer troopers and magistrates’ trusted supporters on the other, would fuel the national debate in the months to come, both about what happened and who was responsible for the violence.

As the vast crowd gathered, the magistrates watched anxiously from the upper floor of a neighbouring private building. Hunt eventually arrived in an open-topped barouche carriage, to great cheers, at 1.15pm. Beside the coachman sat Mary Fildes, organiser of the Manchester committee of female reformers, dressed in white and waving a flag: “She was a remarkably good figure and well dressed, it was very justly considered that she added much to the beauty of the scene,” Hunt wrote lubriciously in his memoirs.

“The moment that I entered the field, 10 or 12 bands struck up the same tune, ‘See the conquering hero comes’ … and from the multitude burst forth such a shout of welcome as never before hailed the ears of an individual,” he went on. A way was cleared for him to get to the hustings platform.

Two lines of special constables – loyalist civilians signed up specially for the occasion – had formed, making an aisle from the magistrates’ house to the hustings, where the carts were then repositioned slightly so that Hunt did not have to bellow into the wind, and the constables became submerged in the crowd. It was at this point that the magistrates either panicked, or put into operation a prearranged plan.

Hay, one of the volunteer magistrates, wrote to Sidmouth later that day, as a justification, that the magistrates had “felt a decided conviction that the whole bore the appearance of insurrection; that the array was such as to terrify all the king’s subjects and was such as no legitimate purpose could justify”. A group of loyalists were asked to sign an affidavit that they believed the town was in danger, and a warrant for the arrest of Hunt and several other organisers was drawn up. Nadin was told by the magistrates to serve it, and asked for military help from the yeomanry to enable him to get to the hustings.

The Massacre of Peterloo! or a Specimen of English Liberty by JL Marks. Photograph: The Art Archive/Rex/Shutterstock

Hunt got out no more than a few sentences before he saw the mounted Manchester Yeomanry approaching the edge of the crowd at a fast pace. They were the first troops to be called. They had been milling in the back streets, drinking in local taverns, and were fired up, ready to unleash themselves on the subversives. They clattered down Cooper Street, knocking over a 23-year-old woman, also called Fildes, and knocking her baby son, William, out of her arms, on to the cobbles and under their horses’ hooves: he was the first fatality of the day. Outside the magistrates’ house, they drew up and cheered, waving their sabres in the air. Members of the crowd initially cheered back, but then a cry of “Soldiers! The soldiers!” spread. Hunt called out: “Stand firm my friends! You see they are in disorder already. This is a trick. Give them three cheers.”

The yeomanry plunged into the crowd at a gallop, attempting to accompany Nadin to the hustings. As they lost order in the crush, they started lashing out with their sabres in order to clear a path. Among those slashed were several special constables. Watching from a window, the Rev Edward Stanley, rector of Alderley who had ridden into Manchester that morning on business, wrote later that they had been in great disorder: “Their sabres glistened in the air … they soon increased their speed and with a zeal and ardour which might naturally be expected from men acting with delegated power … continued their course, seeming individually to vie with each other who should be first.

“As the cavalry approached the dense mass of people, they used their utmost efforts to escape, but so closely were they pressed in opposite directions by the soldiers, the special constables, the position of the hustings and their own immense numbers that immediate escape was impossible.”

When their commander, Hugh Birley, arrived at the hustings, he attempted to arrest Hunt, who said he would only surrender to the civil power, and gave himself up to Nadin. He was pushed from the platform and along what remained of the line of constables to the magistrates house, where he was felled by a blow to the head while being pushed up the entrance steps. The women’s suffrage campaigner Mary Fildes leaped from the cart and was battered around the head by constables. She would go into hiding for a fortnight to avoid arrest. Tyas, the Times’s correspondent, was also taken into custody, as was the radical Samuel Bamford, even though he had played no active part besides being a witness.

The regular Hussar troops had also been mobilised, and their commander Col Guy L’Estrange now trotted over to the magistrates’ house and, looking up at the anxious faces in the first-floor window, asked what he was to do. Hulton shouted down: “Good God, sir! Do you not see how they are attacking the yeomanry? Disperse the crowd!”

In the melee, the yeomanry were hacking at the banners around the hustings and shouting: “Have at their flags!” They were particularly incensed by the woollen red liberty caps – symbols of the French revolutionaries – dangling from the poles. Now, as the yeomanry became engulfed in the melee, the Hussars charged in after them and the crowd began to flee as best they could, screaming in terror and tripping over each other. Behind them, the troops were striking out with their sabres. When the crowd reached the streets at the ends of the field, they found them partially blocked by infantry. Some took refuge in the yard surrounding the Quaker chapel, only to find troops riding in after them. Others were crushed against walls or fell down cellar steps into the basements of the surrounding buildings. Onlookers could see victims lying still on the ground, and wounded people attempting to crawl away through the debris of abandoned shoes, clothes, hats, banners and musical instruments. Within 20 minutes of the first attack, the field had been cleared.

‘The charge … swept this mingled mass of human beings before it: people, yeomen and constables in their confused attempts to escape ran one over the other … the fugitives were literally piled up to a considerable elevation above the level of the ground,” Lt William Jolliffe of the Hussars later wrote. “The Hussars drove the people forward with the flats of their swords but sometimes, as is almost inevitably the case when men are placed in such situations, the edge was used … I must still consider that it redounds to the humane forbearance of the men of the 15th that more wounds were not received.”

It was the crowd’s own fault, the loyalists claimed: “With a factious perverseness peculiarly their own, they have set at open defiance the timely warnings of the magistrates … the revolutionary attempts of this base junto was no longer to be tolerated,” proclaimed one broadsheet report the following day. The magistrates later insisted that they had read the Riot Act, ordering the crowd to disperse, but if they did so few could have heard them – and they certainly did not allow an hour for the crowd to disperse as the law ordained.

The crowd was left to crawl home. “All the roads leading from Manchester to Ashton, Stockport, Cheadle, Bury, Bolton are covered with wounded stragglers,” the Star reported the following day. “There are 17 wounded persons along the Stockport Road, 13-14 on the Ashton road, at least 20 on the Oldham road, seven or eight on the Rochdale road besides several others on the roads to Liverpool.”

Some would conceal their injuries for fear of retribution from employers. But 654 people were sufficiently injured to require medical treatment. The figure is that precise because, in the following weeks, names, addresses and details of injuries were drawn up by newspapers, radicals and a relief committee set up to raise funds to help the wounded and their families. Contrary to the assertions of the authorities, fewer than a quarter were crushed in the crowd: more than 200 were sabred, 70 battered by truncheons, and 188 trampled by horses.

Many of the injured were children, or men and women with families and jobs, of middle age and older. At least two fatalities were special constables. Some died on the spot, others lingered for weeks. The wounds were ghastly: deep sabre cuts to the head and arms, a nose nearly cut off, one man driven into a lime pit and burned, “a piece the size of a half crown clean off the head” of another.

William Marsh, aged 57, suffered a “sabre cut on back of the head, body crushed, bone shattered in left leg”. Three of his six children worked at a factory owned by Birley, the commander of the yeomanry; when Birley heard about Marsh’s injuries, he sacked them. Many of the injured knew their attackers and could identify them, but it did them little good. When one of the most vicious, Edward Meagher, later fired at a crowd that was mocking him outside his house, he was acquitted by the magistrates.

John Brierley of Saddleworth, aged 31, was trampled by the horses and crushed, but his lunch of bread and cheese, which he was keeping in his hat, saved him when a sabre cleft through it. James Lees, 25, had fought at Waterloo and was now a weaver with two children. He received two deep sabre cuts to the head, but when he went to the infirmary a doctor asked him whether he had had enough of political meetings. Lees said no, and was promptly turned away. Before he died, three weeks later, he told a relative: “At Waterloo there was man to man, but here it was downright murder.”

As the troops rallied after the meeting, Hay led three cheers for them. A few days later, the Prince Regent sent a message recording his “great satisfaction at their prompt, decisive and efficient measures for the preservation of the public tranquillity.” The authorities invited selected supporters – loyalists who would back their evidence – to a private meeting at the police office to offer a vote of thanks to the military: “The yeomanry had merited the entire approbation of all the respectable inhabitants of this large and populous town.” This prompted 300 other citizens to complain: “We feel it our bounden duty to protest and to express our utter disapprobation of the unexpected and unnecessary violence by which the assembly was dispersed.”

What had happened could not be covered up, since there had been so many witnesses, but it could be squashed. The authorities tried to claim that the troops had been attacked first with stones and cudgels, though this did not explain why they sabred women and children who were standing close to them or trying to escape. The inquest to the death of Lees, whose head injuries had been untreated, was adjourned in confusion, and a later case brought against Birley and members of the yeomanry resulted in their acquittal on the grounds that they had done their duty in dispersing an unlawful assembly.

A relief committee raised £3,408 to help the wounded, but they saw little of it: more than £2,200 went to lawyers representing Hunt and his fellow accused. Most of the wounded received £2 or less: Marsh and Brierley received £1 each, and Lees’ family £2.

In March 1820, rather to the surprise of the judge, who had summed up for an acquittal, Hunt and his colleagues were convicted, after a trial in York, on a charge of unlawful and seditious assembling for the purpose of exciting discontent. No evidence had been allowed about the way the meeting had been attacked. Hunt was sentenced to two and a half years at Ilchester jail, where he set about writing his memoirs. Johnson, Bamford and two others were imprisoned for a year.

A still from Peterloo, directed by Mike Leigh, which will be released later this year. Photograph: Simon Mein

Peterloo and its aftermath shocked the nation, but did not lead directly to parliamentary reform, as the authorities closed ranks against any change. As the Duke of Wellington later warned: “Beginning reform is beginning revolution.” It would be another 13 years before a limited measure of parliamentary reform was passed – and that would not give the sort of people in the crowd at Peterloo the vote either. Working men would have to wait many decades for that, and women would not get the vote for another century, until 1918.

Peterloo remains a milestone in the long road to political reform, which stretched by slow, incremental changes across the 19th and into the 20th centuries. Hannah Barker, professor of British history at Manchester University, said: “Peterloo was one of the major events in Manchester’s history, and it became a national event almost immediately too, commemorated in vivid cartoons, on plates and teapots and even on handkerchiefs. It was a symbol of the struggle for democracy against state suppression and the fight of ordinary people for civil rights and liberties – these are still important issues today.”

You have to look quite hard for evidence of the most important political event ever to take place in Manchester. There is a circular memorial plaque high on the wall of the Free Trade Hall, and the People’s History Museum on the other side of the city centre has a small display of artefacts, including two sabres that reputedly belonged to a member of the yeomanry from Droylesden. Small memorial ceremonies are held each year on the anniversary. Plans are afoot to stage events on the bicentenary in August 2019. There will be academic conferences and learning packs for schools, and a memorial has been commissioned, to be created by the conceptual artist Jeremy Deller. It all seems a little low-key. Perhaps the moment when the memory of Peterloo will be most stirred will be the release of a film that director Mike Leigh – who was brought up in Salford – is making about the massacre.

“Is Peterloo still important?” asks Jonathan Schofield, who blogs and leads guided tours of the city. “People died for the vote here. They died because they thought it was important to take part.”

The massacre deflected the movement for political reform into a crusade for justice for the victims: “How were boots on the ground expected to translate into political change?” wrote the historian Robert Poole in his book Return to Peterloo. “Had the Manchester meeting demonstrated, to the amazement of high Tories, that large numbers of working people could rally peacefully for a political purpose, what would the reformers’ next step have been? One thing we don’t know about Peterloo is what would have happened if it hadn’t happened, for we are still living with its aftermath.”

• Follow the Long Read on Twitter at @gdnlongread, or sign up to the long read weekly email here.

• This article was amended on 9 January 2018. An earlier version referred to spinning looms where machinery was meant.

