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 .
The Protestant march passes through a mainly Catholic city . Saturday 's march is the largest by the Apprentice Boys group . Comment: