About 15,000 Protestants paraded through this predominantly Roman Catholic city Saturday following a night of Catholic rioting, but the parade itself ended without any direct clashes between rival mobs.

The Police Service of Northern Ireland said rioters in the Bogside, the major Catholic district beside central Londonderry, hijacked and burned at least two cars and threw about 50 Molotov cocktails at police, who were wearing flame-retardant suits, body armor and helmets. Nobody was reported injured.

The trouble came hours before Saturday's parade in Londonderry by the Apprentice Boys, the city's major Protestant fraternal group. Their annual march through Londonderry's central square and atop its 17th-century walls, which overlook the Catholic Bogside, has frequently inspired violent clashes in the past.

But on Saturday, about 700 police officers kept the Protestant paraders — about 10,000 Apprentice Boys and about 5,000 members of approximately 130 accompanying bands — apart from Bogside Catholics opposed to the march. On opposite sides of the central square, police erected high tarpaulin screens to prevent Catholic protesters from being able to see the drum-thumping procession, or for Protestant celebrants to be able to see the Catholic crowd.

Police said the screens appeared to have deterred direct conflicts between rival groups, who in past years have traded salvos of bricks, bottles and other objects across the square.

But once the screens came down, the rival groups hurled stones and bottles. A Catholic youth also threw a Molotov cocktail at a police armored vehicle but, again, nobody was reported injured.

Police said they arrested six people for riotous or violently drunken behavior, but didn't specify whether those arrested were Catholic or Protestant.

Overall, the day went unusually peacefully, according to the commander of the police operation, Superintendent David Hanna.

"I'm very, very pleased," Hanna said. "All the hard work that's been done on the ground to lessen tensions on both sides is paying off."

The Apprentice Boys' annual march commemorates the city's survival during a 1689 siege by forces loyal to the deposed Catholic king of England, James II. The group is named in honor of 13 teenage apprentices, all Protestants, who bolted the city gates in front of the advancing Catholic forces at the start of the 105-day siege.

Clashes between Catholics and Northern Ireland's predominantly Protestant police force during the Apprentice Boys' march in August 1969 forced Britain to deploy its troops to Northern Ireland as peacekeepers. That move, in turn, triggered the rise of the modern Irish Republican Army.