Belfast, Northern Ireland (CNN) -- Security was tight in Northern Ireland on Saturday for a contentious annual march by a Protestant group.
Saturday's march by the Apprentice Boys through the mainly Catholic city of Londonderry is the largest of several they hold during the year, mainly in summer. The march commemorates the Siege of Derry in 1689, when thousands of Protestants died.
Before the Londonderry parade was due to begin at 12:30 p.m. (7:30 a.m. ET), local members were also holding smaller "feeder" parades in their own areas.
A feeder parade in the Ardoyne area of north Belfast, a flashpoint for sectarian violence, happened peacefully Saturday morning.
Trouble flared in Ardoyne and other areas of Belfast last month after a decision to allow another Protestant parade to pass through a mainly Catholic neighborhood on July 12, a day when Protestants march to celebrate the victory of England's King William III over his ousted Catholic predecessor, James II, in 1689.
Dozens of officers were hurt in days of violence surrounding the annual event, known as The Twelfth.
Journalist Peter Taggart contributed to this report.