By contrast, the Lithgow Zig Zag railway, built between 1866 and 1869, required much heavier engineering, including four large rock cuttings, three fine stone viaducts with 30 feet semi-circular arches (originally four were planned, but one was built as an embankment instead) and a short tunnel (three tunnels were planned, but two were daylighted during construction due to leaks, becoming two of the four cuttings mentioned above).