Image caption The main parade in Belfast began at about 1030 BST

Orange Grand Master Edward Stevenson has called on Protestants and Orangemen to engage with the Historical Enquiries Team in murder investigations.

He was speaking in Limavady about the legacy of the Troubles as Orangemen across Northern Ireland held their annual Twelfth of July celebrations.

The Protestant Orange Order took part in demonstrations at 18 venues.

Mr Stevenson spoke at the parade in Limavady. The marches commemorate the Battle of the Boyne in 1690.

This was when Prince William of Orange claimed victory over Catholic King James II.

The principal venues for the 2011 parades were Randalstown, Aghalee, Cullybackey, Ballymena, Broughshane, Ballycastle, Killylea, Barnetts Demesne, Rathfriland, Ballymartin, Holywood, Comber, Lisnaskea, Ballyronan, Limavady, Stewartstown, Sixmilecross and Clogher.

The Twelfth of July is a bank holiday in Northern Ireland.

It is the annual high point of the loyal orders' parading calendar.

Some marches have been a source of tension between nationalists who see the parades as triumphalist and intimidating, and Orangemen who believe it is their right to walk on public roads.

In recent years, the order has made efforts to rebrand the day as "Orangefest," with some believing the event has the potential to become a major tourist attraction.