Sandstone viaducts

The three sandstone viaducts that form a critical part of the Zig Zag Railway are probably the famous and photographed sights next to our steam engines.

Despite being built between 1866 and 1869, they were actually built using the metric scale rather than the traditional imperial and were the largest metric structures in the southern hemisphere at the time of their construction!

The sandstone, which was sourced from a quarry in Lithgow, was originally pure white when the viaducts were built, providing quite the site against the landscape. The weep holes drilled into the stone in certain areas allow water to drain from inside the viaduct, contributing to the magnificent, weathered look we have today.


Despite being over 150 years old, the viaducts actually get stronger as time goes on as the stone naturally cements together over time.


There is, in fact, a ‘half’ or mini-viaduct also built along our line, and there were at least two other viaducts proposed in the original plans, one above the depot, which was turned into a retaining wall and one between number 3 and Belmore tunnel. We can see evidence of this in old photos, where the different coloured fills are obvious.


Part of the work to bring Zig Zag back to passenger services included having the keystone on number one viaduct repaired, new pointing and some restorative work on other stones completed. Zig Zag Railway is grateful to the NSW Government for the grant funding to complete this important work. 


The sandstone viaducts are all heritage-listed, helping us to preserve these structures for future generations.


Key statistics

No. 1 Viaduct, 7 arches, 2 x 4.57m (15′), 5 x 9.14m (30′), on a 201.2m (10 chains) curve, with a maximum height of 14m., (46′), c. 82m (270′ – 90 yards) long.

No. 2 Viaduct, 9 arches of 9.14m (30′) each on a straight alignment, with a maximum height of 23.16m. (76′), 99m. (330′ – 110 yards) long.

No. 3 Viaduct, 8 arches of 9.14m (30′) each, on a 140m (7 chain) curve, 91m. (300′ – 100 yards) long.

‘Half Viaduct‘, at Top Points. Originally top Point Wing Viaduct, (single 30’ arch). In 1895 the inner side was taken down and the area filled in.