To the sound of pipes and drums, some 15,000 members of the Apprentice Boys order paraded through Northern Ireland's second city, Londonderry on Saturday, to commemorate the 1689 survival of a Protestant garrison besieged by Catholic forces.

Marching bands led several hundred members of the order on their annual march around Londonderry's medieval stone walls to celebrate the relief of the city by Protestant troops.

Police reported minor altercations, including petrol bombs hurled at police vehicles in a Catholic neighborhoud of the city, but no injuries.

Three people were arrested for minor offenses, and a bread van was set on fire after about 100 Catholic demonstrators confronted a small feeder march outside the city.

Earlier, police prevented another feeder march from passing through the largely Catholic Ardoyne district of Belfast.

Last month, 25 police officers were wounded in clashes with Catholic residents of the Ardoyne during the annual 12 July march by the Orange Order, another Protestant brotherhood.

The Apprentice Boys

After handing in a letter to police protesting the ban, the Apprentice Boys were bused through the area under police escort on their way to the Londonderry demonstration.

"We had no alternative but to comply," said spokesman Tommy Cheevers.

"We're not in the business of bringing people out on the streets to cause trouble."

Sectarian tensions run at their highest during Northern Ireland's summer "marching season," when hard-line Protestants hold dozens of parades.

The Apprentice Boys order is named in honor of 13 teenage craftsmen who bolted the gates of the walled center of Londonderry as forces loyal to James II, the recently deposed Catholic king of England, approached the city.

The Protestant residents withstood a 105-day siege, eating rats to survive, before a relief convoy from the Protestant King William of Orange sailed up the city's Foyle River on 12 August 1689, and forced James' inept army to flee.