An armoured car spewed a jet of water and spray over the barbed-wire barrier towards the chanting crowd in William Street carrying the Civil Rights Association banner.
Smoke billowed over the cinder-blackened street as shouts of anger, insults and "stones" were hurled at the uniformed and helmeted men carrying self-loading rifles who held the line behind the barrier.
There were surreal moments yesterday in Derry as the street battle scenes of 29 years ago were brought to life again. Then peace was declared, and soldiers and rioters clustered together to share mugs of tea and a smoke.
The re-enactment of some of the events of Bloody Sunday for a television drama-documentary was all the more surreal because just 50 yards away in the city's Guildhall a solemn legal assembly was continuing its protracted inquiry into the 1972 killing and wounding of civilians by the British army.
Shoppers paused to watch with curiosity as filming took place at the site of the army's Barrier 14, the blockade put in place to prevent the Civil Rights march on January 30th, 1972, from reaching its intended destination in the city centre.
It was at this barrier that 20 minutes of intense rioting preceded the invasion of the Bogside by units of the 1st Battalion of the Parachute Regiment who then shot dead 13 people and wounded at least 14 in a sustained period of high-velocity firing.
For those who had been present at the real thing, yesterday's restaging had obvious weaknesses. The few mud-spattered army-type vehicles assembled in William Street were a pale shadow of the huge and deadly armoured force that deployed around the Bogside that day.
The makeshift "water cannon" used yesterday, operating with the aid of hoses linked to the water mains, was a poor imitation of the massive vehicle that trained a powerful jet of purple-dyed liquid on the rioters on Bloody Sunday.
But the actors and extras made up for this in their ferocious enthusiasm during the action scenes. Foam and polystyrene "rocks" rained down on the "soldiers" and "RUC officers" behind the barrier, and deafening volleys of blanks were fired back from mock rubber-bullet guns.
An artificial smoke machine wafted clouds of vapour across William Street, which had many of its buildings repainted as they were in 1972 - walls were blackened and windows boarded up or covered with corrugated sheets.
But this film-set smoke bore no comparison with the clouds of acrid CS gas that left scores of people choking, vomiting and half-blinded on Bloody Sunday. Nor could the film-makers recreate the genuine sense of menace engendered by the military snipers posted in every skylight and on ledges and flat roofs along the fringe of the Bogside on that fateful afternoon.
As far as they went, however, the scenes were authentic and the action not only proved an eye-opener for a generation of onlookers born since Bloody Sunday, but also impressed some local veterans. "It was excellent," said Mr John Kelly, of the Bloody Sunday Trust, whose brother, Michael, was shot dead on the day. "To see the young boys coming down and pegging away, the water cannon and so on . . . it was very well done."
He admitted the sight of the red berets of paratroopers on Derry's streets yesterday caused a certain frisson - "It brought back that little bit of anger."
The film is being made by Sunday Productions for Channel 4 television, and the script is by Jimmy McGovern, scriptwriter of Cracker and a number of major drama-documentaries.
Families of the Bloody Sunday victims were consulted in the process. Moving scenes are expected tomorrow evening when the filmmakers restage the bringing of the coffins of the Bloody Sunday dead to St Mary's church in the Creggan. Several thousand local people are again expected to participate.
At lunchtime yesterday, several senior lawyers from the Bloody Sunday inquiry, including the tribunal's own counsel, Christopher Clarke QC, strolled over to the location to watch the riot reconstruction. "It will do them no harm to see it," one cynical local observer remarked.