The Mourne Wall

Early evening sunlight highlights the Mourne Wall as it strides over the High Mournes:


Slieve Donard; Slieve Commedagh; Slieve Corragh; Slievenaglogh

There's an interesting article in Wikipedia; here's the first paragraph:

The Mourne Wall is a wall which was constructed to enclose a reservoir's catchment area in the Mourne Mountains, Northern Ireland. It was built between 1904 and 1922 by the Belfast Water Commissioners to enclose the water catchment in the Mournes.
The wall was crafted from natural granite stone using traditional dry stone walling techniques. On average the wall is about 1.5 metres high and 0.8 to 0.9  metres thick. It is 22 miles (35 km) long and passes over fifteen mountains