On GAA: Monday night in Croke Park and the Cusack Stand became a kind of a time-machine for a couple of hours. In the latest of a series of lectures organised by the GAA Museum, a formidable line-up of speakers took a large and absorbed audience back 85 years to the day to the event that most profoundly etched the association into Irish history.

I imagine very few of those present didn't at some stage envisage the scenes that took place directly beneath them on what became known as Bloody Sunday. More fancifully, you could wonder what anyone in that terrified crowd would have made of their surroundings had they been transported more than eight decades into the future to see what the GAA would become.

It has been easy until recent years to criticise the poverty of the association's attention to its history and heritage. But since the opening of the museum in the new Cusack Stand that has changed, and as well as the collection and display of exhibits, the organisation of events such as this week's has greatly enhanced the GAA's ability to look at its history and place it in context.

Monday's lecture was an impressive stage in that process. Bloody Sunday is one of those iconic events that most people understand in broad outline: an outrage against civilians perpetrated as a reprisal for the IRA's most spectacular operation of the War of Independence, the assassination earlier that morning by Michael Collins's hit-squad, known as the Apostles, of 14 men believed to be British agents.

The image of innocent spectators being shot and killed and of a footballer, Michael Hogan, being gunned down and into immortality, is strong and resonant even until today.

Earlier only this year, the debate on Rule 42 was coloured by references to playing British sports on the ground that the Black and Tans (in fact, the Tans weren't involved, and the action was carried out by the equally notorious Auxiliaries) had violated so grievously in 1920.

Whereas these perceptions of the atrocity are not inaccurate, those present on Monday night learned a little more about the context, light and shading of what became a watershed moment in history.

Dr Brian Hanley, of Trinity College, Dublin, opened the lecture by setting the political context of the time, how the arrival of the Black and Tans and Auxiliaries in July of 1920 was acknowledgement of how demoralised the RIC had become in trying to maintain law and order in Ireland.

By November the war was escalating. Terence McSwiney's hunger strike and the execution of Kevin Barry were emotive backdrops to the continuing IRA activity, and the policy of reprisals, widely implemented by British forces, deepened the conflict.

An interesting aside is that of the 14,000 Black and Tans and Auxiliaries, 2,000 were recruited in Ireland, and a substantial number of them were Roman Catholic.

Equally thought-provoking was the questioning of how effective the Bloody Sunday assassinations that morning had been on a military level, in that targets had been missed and a number of others were of no particular intelligence value.

The action also provoked a security clampdown that affected the IRA, and the loss of top operatives Peadar Clancy and Dick McKee, who were shot in reprisal, was also a major blow.

Nonetheless, it was effectively argued that the propaganda coup was significant, undermining for good British assertions that Ireland was under control and that IRA units were mostly drunken murder gangs.

But the most fascinating area was the exploration of the links between the GAA and the IRB. You could be forgiven for casually assuming that the association and the republican movement were inextricably intertwined by 1920, such were the numbers of GAA members active in the Rising and War of Independence.

Yet at an institutional level there was far from a complete overlap. It was pointed out that, according to an account by Todd Andrews, who had been a member, the Dublin Brigade of the IRA was half made up of soccer men. The GAA had refused permission for the Volunteers to drill at Croke Park prior to the Easter Rising of 1916, although political rallies and conventions were subsequently accommodated.

Marcus de Búrca, doyen of GAA historians, admitted in his talk to being "amazed" that the GAA had allowed the Dublin-Tipperary challenge match to go ahead that day. Given the policy of reprisals, a large gathering (between 5,000 and 8,000) in Croke Park must have been an attractive option.

The Auxiliaries are said to have tossed a coin to decide between sacking O'Connell Street and raiding Croke Park. The GAA lost. Ironically, the reason the association proceeded with the match was that it was felt cancellation would imply a link between the GAA and the IRB.

The match wasn't long in progress (on a lighter and familiar note, it started late) when a plane flew low over the ground and gave a Verrey light signal, before heading north, a manoeuvre accepted as the go-ahead for the attack.

After the mayhem had played itself out, 13 were dead or fatally wounded, including Hogan. Three priests tended the Tipperary player at separate times (and many years later a book by one had to be withdrawn and re-printed to correct the impression that he had been the sole comforter).

The Tipperary players were believed, in all likelihood incorrectly, to have provided cover and gunmen for the activities that morning of Collins's squad. Rounded up after the match, most believed they would be shot, but eventually they were released. It was said that they were held hostage while the crowd - or those who hadn't fled - were searched. Had any shots been fired during this process, the Tipp players were to be incrementally killed in retaliation.

Dublin's footballers, many of them from the local O'Toole's club, weren't considered as important to the authorities, although they too had IRA volunteers among their number and they managed to slip away in the confusion.

According to an encyclopaedic talk on the team from Dublin GAA historian Jimmy Wren, two of them were the famous McDonnell brothers, Johnny - who after the match had to dispose of an arms shipment in his house - and Paddy, who in 1917 had founded the St Laurence O'Toole's Drama Society with playwright Seán O'Casey, another present in Croke Park that day.

Historian Diarmuid Ferriter wrapped up the evening by assessing the impact of Bloody Sunday and making the central point that the impact of the carnage - 29 people dead - created the environment both among the British government and public, as well as within the IRB, for peace talks, which duly followed in a matter of months.

It seemed strange to be weighing up dispassionately the ins and outs of an event so integral to GAA mythology in the very place where it happened, the place where the association shed blood for Irish independence. But it was also fascinating and very appropriate.