A BORDER landmark inspired by a mathematical genius and that provided a gateway into a remote area is heading for a milestone anniversary on Sunday, July 1.

Exactly 150 years ago to the day the first train crossed the magnificent multi-arched Kielder Viaduct in Kielder Water & Forest Park, linking Hexham with Riccarton Junction via the now defunct Border Counties Railway line.

Now a day of celebrations is planned by the Northumberland & Newcastle Society to remember one of the great achievements of Victorian engineering.

The Forestry Commission will host talks and displays by local railway heritage groups in Kielder Castle, whilst walkers stride out to retrace the line of the spectacular route through the 62,000 hectare Northumbrian forest.

Crossing the River Tyne was no easy feat for the 19th century architects and arches of huge geometric complexity were required to cope with the skewed alignment of railway and river. The mathematics were solved by Peter Nicholson of Newcastle upon Tyne in the 1840s, a largely self-taught architect, mathematician and engineer who began life as a humble cabinet maker. But while the design pushed the limits of technology, it also had to gain favour with the Duke of Northumberland, so it was built in Baronial style complete with motifs and battlements in keeping with nearby 18th century Kielder Castle.

Sue Howie, Secretary of the Northumberland & Newcastle Society, which purchased the viaduct in the 1960s for the grand sum of �1 to save it from destruction, explained: "It's salutary to think that the viaduct faced demolition 45 years ago after the line was closed by British Rail. Now it is a scheduled monument, a focal point for the community and carries the popular Lakeside Way over the Tyne, so it's still connecting people with places. Our day of celebrations is designed to highlight this magnificent feat of engineering and salute those who played a part in securing its future."

Talks at Kielder Castle by Roger Darsley and David Dunn run from 2pm on 1 July with a buffet and refreshments included in the �10 entry fee. Tickets can be obtained on 0191 2816266 or by emailing at secretary@nandnsociety.co.uk. There will also be a seven mile walk, crossing the viaduct, starting out at 10am. The terrain is fairly easy going and booking is required by contacting Terry Greg on 01434 250 462, or emailing viaduct150@staykielder.co.uk Alex Maclennan, Forestry Commission Public Affairs Manager for the North East, added: "The Victorians never shrunk from an engineering challenge and the sheer scale of Kielder Viaduct still takes the breath away. But it is also remarkably beautiful and has become part of the Border landscape. It's a great time to celebrate a wonderful landmark."