Mourne Mountain Wall being repaired

The wall runs across 15 peaks in the County Down mountains

Northern Ireland's longest listed monument is to be repaired after years of exposure to the elements and damage due to lightning strikes.

The 32-km (20-mile) Mourne Wall runs across 15 peaks in County Down.

But parts have fallen into disrepair due to the weather and Northern Ireland Water, which now owns it, is planning restoration work.

Construction of the wall began in 1904 when it was built to mark the boundary of the catchment for a large reservoir.

The Silent Valley reservoir still supplies drinking water to Belfast and much of County Down.

Construction of the wall began in 1904

It took teams of local stonemasons 18 years to build it by hand, employing a dry stone-walling technique which used no mortar.

This time contractors will helicopter material to almost 400 areas which need to be repaired.

The company had a duty to maintain the wall, said NI Water spokesman Dermott McCurdy.

The work will be carried out by stonemasons from the area under the guidance of the Mourne Heritage Trust and will be overseen by the Northern Ireland Environment Agency.

The work will be carried out by stonemasons from the area under the guidance of the Mourne Heritage Trust

The first phase will concentrate on a 2.5km section between Slieve Loughshannagh and Slieve Meelmore.

NI Water said it would "strive to protect the integrity of one of Northern Ireland's most iconic listed monuments".