Knapsack Gully Viaduct was designed by John Whitton, Engineer-in-Chief for the railways. The seven sandstone arches across Jamison Creek are five and a half metres wide and thirty-eight metres high. Construction began in March 1863 and was completed in May 1865. Up until 1913 when the Glenbrook deviation was built, the Knapsack Gully Viaduct formed part of the Lapstone Zig-Zag. It was reopened to road traffic as part of the Great Western Highway in 1926 and finally closed in the 1990s.
