Why are huge bonfires lit across Northern Ireland on Eleventh Night?

Fire fighters dampen down nearby properties as a huge bonfire in the loyalist Corcrain area of Portadown, Co Armagh, is lit (PA)

Huge bonfires will burn in loyalist areas across Northern Ireland late on Sunday night to usher in the main date in the Protestant loyal order parading season – the Twelfth of July.

Here is an overview of what the event is all about.