The Ebbw Valley posed two significant challenges through its geography:[5] Chief Engineer Charles Liddell concluded that stone would be a poor choice for construction of a suitable bridge, as additional stone would need to be shipped to the valley, and the height of the resulting structure would result in an unstable and high-maintenance bridge.

Further, the solidity of a stone structure would create additional compressed wind flow around the rail tracks, resulting in a possible safety hazard for passengers and train crew.

After shortening the spur from the Monmouthshire and Brecon Canal, and with the land between the two valleys acting as the ninth pier, the first girder was hoisted into place on 3 December 1854.

[3] The viaduct was opened on Whit Monday, 1 June 1857 by Lady Isabella Fitzmaurice, with the first train crossing the bridge and entering the Bryn Tunnel in June 1854,[5] but it could not proceed further as Kennard's construction team had not yet finished the Hengoed Viaduct, which he had won the contract to design and act as civil engineer on.

The NA&HR route, due to a combination of its height and steepness, proved to be one of the most expensive railway lines in all of the UK to operate.

It was therefore no surprise when, following the post-World War II nationalisation, British Railways reduced the entire extension line to single track after 1947.

[5] In the period between closure of the NA&HR and dismantling operation beginning, scenes for the Universal Pictures film Arabesque, which starred Sophia Loren and Gregory Peck, were shot both on and around the viaduct.

[3] The iron parts of the bridge had been completely dismantled by the end of 1967, and only the stone and cast concrete abutments now remain visible on the valley sides.