More than 60 people gathered on New Year’s Day to step out on a walk celebrating the 150th birthday of the Kielder Viaduct.
The Forestry Commission led the guided walk through part of Kielder Water & Forest Park and then across the viaduct.
This year also marks the 150th anniversary of the first train crossing the bridge.
Kielder Viaduct, in Kielder Water & Forest Park, Northumberland, is now a monument and is treasured by local people.
The railway line closed in 1958 and the viaduct, then owned by British Railways, fell into disuse.
Not long after it was earmarked for demolition but was rescued by the Northumberland and Newcastle Society.
Construction on the structure began in 1858 and was finished in 1862 as part of the Borders County Railway. The line connected Hexham, Northumberland, to Riccarton Junction in Dumfries and Galloway.
The viaduct was built in what is termed Baronial style. It has a castellated parapet and false arrow slits and this design was chosen to complement the architecture of Kielder Castle, roughly a mile from the viaduct.
The construction project imposed an enormous challenge for engineers because the rail line crossed the North Tyne river at an angle.
In an article about the viaduct, Newcastle and Northumberland Society member Nigel Jenkins, writes: “When the old North British Railway constructed a line up the North Tyne Valley, the crossing of the river near to the Duke of Northumberland’s shooting lodge at Kielder Castle had to be built on a skew with the line of the river.
“This situation produced arches of great complexity with the stones of each arch gradually changing from aligning with the skew piers to lying at right angles to the line of the bridge at the crown – no mean geometrical problem.”
The complex puzzle was solved by mathematician Peter Nicholson of the Newcastle School of Design.
He created a series of calculations which meant that each stone could be individually shaped to fit the skew design.
Nicholson’s calculations worked out the shape of each individual wedge-shaped stone for each arch so that those at the top would lie at a right angle to the viaduct’s deck allowing for extra strength and stability.
The impressive structure is considered to represent the finest remaining example of the skew arch form of construction.
In 2004, the Newcastle and Northumberland society worked in partnership with Kielder Community Trust on a project to create eight iron panels installed between the parapets.
The panels were forged by six master blacksmiths, who interpreted designs by community groups in Kielder Village and pupils from Kielder First School.
The viaduct is 130 yards long and 55ft high and is part of the £3m Kielder Way, which encircles Kielder Reservoir.
It is an important part of Kielder’s network of footpaths and offers stunning views across the North Tyne and off the flora and fauna close by.