Opened on the 17th November 1872, Lambley Viaduct was the engineering centrepiece of the Newcastle & Carlisle Railway's branch to Alston. Only a single line crossed it - the rest of the route, which had already been in use for several months, was double track.
Originally designed with 24 arches of 20 feet in span, the viaduct was eventually built in three sections separated by large intermediate abutments, presumably as a result of geological problems. It stands as a monument to Sir George Barclay Bruce (1821-1908), the eminent Victorian engineer whose handiwork it is.
Rush & Lawton were the contractors with quarries at Slaggyford and Bardon Mill providing its sandstone. Three of the rock-faced piers stand in the river; triangular cutwaters protect them. They are built of massive stones each weighing up to 500kg and topped with heavy imposts; similar-sized stones in ashlar comprise the main arch voussoirs. A row of block corbels is inserted immediately below the parapet which has sloped coping and terminates in low pyramidal caps.
As built, the structure comprises nine spans of 56 feet over the river, with three smaller arches to the north side and four on a curve at the southern end, all 20-foot spans. Overall, it is 289 yards in length and reaches 108 feet at its highest point; the deck is 11 feet wide. From the north, the trackbed has a rising gradient of 1:170 before levelling slightly to 1:240.
At one time, a pedestrian footbridge crossed the water, supported by the viaduct's piers.
The branch closed in 1976 after which the condition of the structure deteriorated, with some of its stonework falling into the river. It was Grade II* listed in August 1985. A survey was carried out in 1994; over the following two years, it was restored and much of the masonry replaced. Around 3000m2 of lime mortar was imported from France and used to repoint it.
Today Lambley Viaduct accommodates the South Tyne Trail and has to be one of the most elegant viaducts anywhere in the country.