The playful atmosphere serves to deceive. As William of Orange stands triumphant over King James II, sword pressed to his throat, the crowd lets out a roar of appreciation.

Children with excited faces call "Well done King Billy" as muskets, loaded with blank ammunition, are hoisted and fired mercilessly at a green flag carried by the defeated Jacobite troops.

The scene, as anyone from Northern Ireland or the republic well knows, is the conclusion of the historic Battle of the Boyne, re-enacted on Tuesday by followers of the Royal Black Preceptory.

More than 300 years after the Boyne, William of Orange returns

The battle, which took place in 1690, is the most important landmark in the history of Northern Ireland, signifying the triumph of Protestantism over Roman Catholicism.

The rest, as they say, is history. History that hangs heavy over the peace negotiations that are in the balance as unionists debate whether to go forward with devolution despite the IRA's reluctance to give up its weapons.

King William III's victory is the key event celebrated by loyalist communities during the summer marching season.

After the tense build-up to this year's 12 July celebrations, the annual "Sham Fight", as the re-enacted battle is known, was an altogether more predictable affair.

It is preceded by a parade of the Royal Blacks and their associated bands through the rural town of Scarva, where King William and his army camped before moving on to the Boyne.

The preceptory is a sister institution of the Orange Order, but has fewer members because of its more selective membership. One insider described it as a "more dignified, more religious organisation".

The rest is history: King William sets a sword to James II's throat

The main difference is that members, who are all Protestants, sport the same horseshoe-style sashes as their better-known brethren, but in black rather than orange.

All members must already be in the Orange Order before they can join the "Blacks".

An estimated 6,000 "blackmen", with accompanying bands, braved the grey skies and sporadic downpours for this year's march through the narrow streets of Scarva, in County Down.

Thousands more crammed together along pavements and country lanes to watch. Bandsmen and women, dressed in bright immaculate military-style uniforms whipped up stirring tunes to drive the parade.

Men in suits, sashes, bowler hats and "Masonic" aprons, some carrying staffs or maces, wore mostly solemn faces as they trudged the long route to the scene of the re-enactment.

But that was just parade form. At the end there were smiles as marchers mingled with families and friends.

Bill Logan: Stiffened resolve to parades disputes

"In many ways this is more important to some people than the Twelfth," said George Patton, a Royal Black member and executive officer of the Orange Order.

Yet there were underlying tensions. Many of the marchers had paraded with Orange lodges on Monday. Some would have been re-routed on the orders of the Parades Commission.

"It's difficult not to offend those who have a determination to be offended," the newly elected sovereign grand master Bill Logan told the massed crowed from a platform.

Mr Logan also signalled a stiffening of personal resolve towards parade disputes. He told the crowd how he had met with a nationalist residents committee four years ago during a report, but later said he would have reservations about doing it again.

"We are being threatened. Unless we meet with some people, our wishes to walk on the highway will not be granted - threats we do not take kindly to," he said.

Strong words, but not strong enough to ruin King Billy's moment of glory on the day.