Like the past itself, commemoration is fiercely contested in Northern Ireland. Progress has been made to foster a shared history through First World War initiatives, but there remains a long way to go on all fronts.

This makes a forthcoming memorial to Belfast volunteers in the Spanish Civil War (which raged from 1936 to 1939) all the more remarkable. Representatives put aside their traditional differences to back Councillor Pat McCarthy's 2014 motion to establish a stained-glass window at the City Hall, honouring all those who went out to fight for the democratically elected Spanish Republic.

Breaking across sectarian borders, 48 Catholics and Protestants served side by side in the ranks of the International Brigades: a sublime moment of working-class unity in the city's turbulent history.

In the clash between democracy and totalitarianism, most commentators now agree that the Spanish Civil War represented a dry run for the Second World War - except that in Spain, democracy lost. In all senses, these volunteers were ahead of their time.

The window - to be unveiled on November 24 - is courtesy of the International Brigade Commemoration Committee, which has organised a number of schemes across Belfast.

We have all seen the numerous memorials to Belfast's Spanish volunteers, from the familiar statue in Writers' Square, opposite St Anne's Cathedral, to the plaque in The John Hewitt bar (interestingly, Hewitt and his wife, Roberta, took in Basque refugees during the Spanish conflict).

Such spaces are already well-attended in the Short Strand and especially to the west of the city. The International Wall of Northumberland Street, off the Falls Road, has a vivid mural to Belfast volunteers, as well as a plaque to two volunteers from both sides of the divide: William Beattie and Dick O'Neill.

However, the memorial in the City Hall is a different proposition to any of these fine ventures.

The site of many a squabble, from the founding of Northern Ireland unto the present day, Belfast City Council is one of the most divided spaces in the city - indeed, an infamous "bear-pit of sectarianism" - which has played regular host to slanging, stalemate and general wind-up.

Yet, even here, councillors came through to collectively embrace and champion a vital episode of Belfast working-class consensus.

Some are fond of dismissing Belfast's Protestant working class as reactionary, conveniently passing over the individuals who gave their lives for socialism during the Spanish Civil War.

In February 2014, more than 120 people gathered in the Shankill Road Library to pay tribute to seven such men from the area, who were honoured with a plaque.

The remembrance of the "magnificent seven", who were drawn from across the Labour movement, represented part of a wider recovery of the forgotten profile of working-class Protestant radicals.

The Left would do well to acknowledge the radicalism displayed by all parts of the city in the 1930s. Though few had knowledge of the Shankill volunteers, the tendency has been to downplay, or ignore, this vein in unionist parts of the city.

But unionists and loyalists, too, appear to have deliberately forgotten that their tradition is a broad church, which includes labour and Left politics.

Councillor Jeff Dudgeon is aware of this heritage and has played a role with other unionists in bringing the City Hall monument to fruition. The people of the Shankill also know better; at the February 2014 event there was standing room only.

A key individual bridging the labour movement in Northern Ireland to the Spanish conflict was Harry Midgley.

After serving on the Western Front, he represented jobless ex-servicemen at City Hall during a time of high unemployment and short-time working in linen and engineering.

Midgley drew support from both communities during his election for Dock in 1933, but his support for the Second Spanish Republic and resulting confrontation with the anti-socialist Catholic Church - as well as the Irish News, both of which endorsed the nationalist leader General Franco - cost him the seat in the 1938 election.

Midgley is still a controversial figure. The revival of debates around him at the February 2014 event on the Shankill provoked an odd reaction from the floor. The historian Graham Walker argues that Midgley "was never to forgive, or forget" the experience of requiring police protection just to give speeches criticising Franco.

Indeed, it may be seen that Midgley's journey from labour radical to hardline unionist was as a direct result of the personal attacks he endured for supporting the democratically-elected Spanish Republic.

Certainly, his later statements as a unionist cabinet minister pointlessly insulted Catholics, but they did not detract from his early Labour career, or integrity over Spain, a battle he - unlike his opponents at the time and since - was on the right side of.

Finally recognised for his Spanish stance, Midgley is one of several individuals named on the stained-glass monument. Also featured are Betty Sinclair, Sam Haslett and Sadie Menzies. Sinclair was an Ardoyne-born Protestant who had been prominent in the outdoor relief strike of October 1932: one of the few times when mutual poverty briefly overwhelmed Northern Ireland's tribal divisions and led to cross-community protests on the streets.

Continuing to work tirelessly in public life, Sinclair involved herself in the civil rights campaign of the late-1960s, holding to the doomed hope that the working class would not split along the violent, sectarian lines she herself had witnessed in the 1920s.

Some will question why public money is being used on this project at a time of cuts and pressured finances.

The reason is that Belfast remains a divided city, divided in large part because of a history which saw the working classes of both communities in violent conflict with one another.

We have all to remember a little differently and through the Spanish conflict - where Catholic and Protestant fought as one against the onslaught of fascism - we have precisely such an example.

Also inscribed on the window is a poem specially written by Sam Burnside, which ends: "We must remember them - and live. No Pasaran."

The last phrase, translated as "They shall not pass", was the defiant rallying cry of the International Brigades.

Though they lost militarily, as we continue to remember the volunteers from across Belfast who expired in the Spanish dust, the democratic values they fought for ultimately prevailed.

We can all say: "No Pasaran."

Dr Connal Parr lectures in modern history at Hertford College, Oxford

Belfast Telegraph