The Mourne Wall (Irish: Balla an Mhúrn) was constructed to enclose a catchment area of the Silent Valley Reservoir in the Mourne Mountains, Northern Ireland. The 1.5 m (4 ft 11 in) high stone wall, which was built to keep livestock from contaminating water supplies, took almost twenty years to complete (1904 to 1922). The project was overseen by the Belfast City and District Water Commissioners.