The South Durham & Lancashire Union Railway fought its way over Stainmore Summit, 1,370 feet above sea level. Opened on 4th July 1861 as a single-track route, the steep western descent into Kirkby Stephen took it over three masonry viaducts - Hatygill, Merrygill and Podgill - all engineered by Sir Thomas Bouch.
The latter of these was the most substantial, with 11 arches each 30 feet in span. It conveyed the line across Ladthwaite Beck for a distance of 155 yards, reaching 84 feet high at its peak.
Built by contractor Chambers & Hilton for £6,189, the inside faces of the piers still have projecting stones at the top, used to support the timber centering for construction of the arches.
The route was an immediate success and, during the 1880s, was hauling a million tonnes of coke annually to Cumbria's coastal blast furnesses. Between 1889-92, to satisfy this demand, a second line was added to carry westbound trains. This involved building a second viaduct to the south side of the first, then tying the two together. The complete structure is 25'7" wide.
Seven sections of parapet were removed to create refuges, with cast iron plates inserted flush with the outer edge of the stonework. Both abutments feature pilasters, topped by monumental stones cut into pyramid shapes.
The through route closed in 1962 but a short section survived until 1975 to serve Hartley Quarry - this involving crossing Podgill Viaduct.
The structure - now Grade II listed - was acquired by the Northern Viaduct Trust in 2000. A restoration programme was initiated which involved repairs to the masonry, waterproofing of the deck and raising its surface by 300mm. It now forms part of the Trust's 'railway trail'.