The construction of George Stephenson’s 1825 Stockton and Darlington line has to be considered in two distinct phases.The first being the 5.80 miles from Witton Park Colliery (Phoenix Pit ) to New Shildon. This hilly section traverses the two high watersheds known as the Etherley and Brusselton ridges, seperated by the river Gaunless, a tributary of the river Wear. The second some 19.60 miles long from New Shildon to Stockton, via Darlington, was relatively level and ideal for locomotion haulage.
It was the 5.80 mile section that presented the major engineering challenges. The gradients of this first section were such that locomotive haulage was ruled out from the start and consequently the a need for inclined planes, operating in conjunction with horses, was crucial to the effective running of the railway; with static steam powered engine houses located on the Etherley and Brusselton summits. The use of inclined planes, in conjunction with stationary steam powered engines and rope haulage, was already established at the time and George Stephenson himself had experience at Willington Quay, Killingworth and on the Hetton Colliery Railway.
Where the line crossed the river Gaunless George Stephenson designed and constructed the world’s first cast/wrought iron railway bridge. A highly innovative design for its day it incorporated both arch support and suspension bridge principles.