'Bloody Sunday' - an introduction
Thirteen people were killed after members of the British Army's Parachute Regiment opened fire on a civil rights march in the Bogside area of Derry on 30 January 1972.
Seventeen people were injured.
The day became known as Bloody Sunday.
About 10,000 people took part in the march, which was organised by the Northern Ireland Civil Rights Association to protest against the policy of internment without trial.
The march took place in an atmosphere of heightened tension.
The previous weekend, an anti-internment march at Magilligan Strand had been halted by members of the Parachute Regiment, who fired rubber bullets and CS gas at the crowd, and there were fears that violence would erupt again on 30 January.
Like all civil rights marches, it was illegal because the Northern Ireland government had banned such protests.
The march begins
The marchers gathered at Bishop's Field in Creggan at about 2pm to walk to the Guildhall Square in the city centre, where a rally would be held.
As the marchers approached the city centre they were blocked by army barricades.
The organisers led most of the demonstrators down Rossville Street towards Free Derry Corner, but some stayed behind at the barricade on William Street to confront the soldiers.
Stones and other missiles were thrown, and the soldiers responded with CS gas and rubber bullets before drenching them with a water cannon.
The first shots the soldiers fired injured Damien Donaghy and John Johnston, who died later.
The Parachute Regiment then advanced into the Bogside, with orders to arrest as many of the civil rights marchers as possible.
The soldiers claimed they were fired upon from Rossville Flats as they moved in to make the arrests and they then returned fire, but the marchers said the paratroopers on the ground and army snipers on the city walls above the Bogside shot indiscriminately at unarmed civilians.
Many of the victims were shot dead while fleeing from the army or going to the aid of the wounded.
Thirteen of the marchers were killed and 17 injured.
The events of Bloody Sunday caused shock and revulsion across the world. In Dublin, a crowd of protesters burnt the British Embassy.
In Northern Ireland, it marked the effective end of the non-violent campaign for civil rights.
Many young people who had previously regarded themselves as non-political joined the IRA.
Two months after Bloody Sunday, the Stormont parliament which had ruled Northern Ireland since its creation in the 1920s was suspended and direct rule from London was imposed.
In April, the Widgery Inquiry concluded that the Paratroopers' firing had "bordered on the reckless".
It also concluded the soldiers had been fired upon first and some of the victims had handled weapons, despite evidence from witnesses who said the victims were unarmed civilians.
The Catholic community rejected these findings as a "whitewash" and began a long campaign for another inquiry.
In 1998 a fresh inquiry, headed by Lord Saville, was announced.