It was built for the Kilmarnock and Troon Railway, opened in 1812; the line was a horse drawn plateway (although locomotive traction was tried later).

[3] The arches were of local freestone with sandstone ashlar facings and rounded cutwaters: these were later extended to form semi-circular buttresses.

[3] Hollis was refused permission to dismantle part of the mill dam to lower water level for pier construction, and "in July 1809 he was authorized to proceed by means of a cofferdam, involving 'very little more expense', with the advantage that 'the stones for the bridge can be floated down on a punt'.

"[7] Paxton suggests that the original standard of construction was poor: This utilitarian, medium-scale viaduct was designed in accordance with traditional rather than 1810 state-of-the-art practice.

It had become obvious that the structure was near to collapse, and in February 1992 the Laigh Milton Viaduct Conservation Project was formed.

When it was by-passed, it remained in place, and was used as a footway and possibly for cartage to and from the pit on the west side of the river, Fairlie Colliery No.

This second bridge was wooden; it was located where the river banks were lower than at the first viaduct, and elevated approaches were needed.

In 1807 the Marquess of Titchfield (later the 4th Duke of Portland) commissioned William Jessop to build a railway line between Kilmarnock and Troon.

Laigh Milton Viaduct was located on a sharp curve, and the conversion work included the provision of a new structure a short distance to the south.

The GPK&AR was taken over by the Glasgow and South Western Railway and the line remains in use today (2013), owned by Network Rail.

Ownership proved difficult to trace, but was eventually found to rest with adjoining farm owners, and the viaduct was purchased from them for a nominal sum.

Paxton records that The viaduct had become fragile largely because of crumbling of much of its stone, which was not of the best quality, being of a minutely fissured weak texture.

With lack of maintenance, vegetation and weather effects this weakness had led to widespread stone loss and serious undercutting to all piers at or near water level.

Some movement had occurred long ago causing stretching and hogging of the arches adjoining the west pier.

The north spandrel wall had suffered extensive stone loss at the top and some peeling away of pier bull-noses.

The preservation of the 300 mm distortion of arch 2 was maintained; the light coloured railings are unobtrusive visually against the sky.

The 1911 Ordnance Survey map marks the trackbed alignment of the first and second bridges, whilst the 1860 mineral line to Thorntoun and Gatehead collieries is now shown as a footpath.

No sign of the wooden viaduct is indicated and a saw mill is now marked, possibly the cause of the need for the extra definition of the name of the site.

A 'Gatehead Toll Bar' is still marked on the road down to Laigh Milton mill and the Craig house estate on the 1860 OS map.