The last rivet was secured, the bridge was complete, and Dublin and Belfast were finally, formally and officially connected, writes Mary Mulvihill.
That was exactly 150 years ago, on April 30th 1855, when the Boyne estuary at Drogheda was bridged, and the Dublin-Drogheda and Drogheda-Belfast railway lines were welded together into one seamless Dublin-Belfast line.
But this was no ordinary bridge. It was, in fact, a pioneering feat of engineering and a world first. And engineers from around the world came to admire it.
What they were marvelling at was the bridge's mid-section: a wrought iron lattice structure, 155 metres long and soaring 30 metres above the river. This was the longest of its kind in the world, and a daring piece of engineering: no one else had ever attempted such a long, lightweight, wrought iron structure. Furthermore, it was expected to carry heavy trains.
The design was the brainchild of the railway engineer Sir John MacNeill, who had been inspired by the timber lattice bridges used in the US. MacNeill realised that, if a similar lattice structure could be built in metal, it would be stronger and could span wider crossings.
In 1843, he built a small wrought iron test bridge at Clontarf, and the following year built one with a span of 44 metres across the Royal Canal north of Amiens Street (now Connolly) railway station. This "proof of concept" convinced him the approach was perfect for the challenge of building a railway bridge across the Boyne estuary.
The problem is that the Boyne estuary is deep and wide, with a particularly steep drop on the southern side. And trains do not like steep drops. They prefer a level run, or at most a gentle gradient. So any railway bridge would have to stay high above the river, and therefore span the full 550 metres of the estuary. Happily, this high-and-wide approach also suited the Admiralty, since it allowed tall-masted ships to pass under the bridge.
Building a bridge capable of carrying a fully-laden train proved an arduous undertaking, especially securing the foundations in the soft river bed, as the piers had to be massive enough to carry the weight of both the bridge and a train. Quite a challenge in 1852.
By then, the Dublin-Drogheda line terminated on the Boyne's southern shore and the line down from Belfast had reached the river's northern bank. Passengers wanting to continue their journey had to cross the river by horse and carriage, or on foot, from one railway terminus to the other, and the full Dublin-Belfast journey could take eight hours.
Work on a connecting bridge began in 1852. But workers digging the foundations for the mid-river pier dug ever deeper into the soft mud, and ever deeper into trouble. After 10 metres they still had not hit firm ground, and in 1853 the contractor, William Evans, went bankrupt.
Despite that, he honourably mortgaged everything he had and converted the timber scaffolding into a temporary bridge so that trains could make the through run, albeit at only 4mph, for the Great International Exhibition that was taking place in Dublin that summer.
Digging continued for another five metres before a foundation was reached, and it was another two years before the final rivet was secured and the bridge officially opened. The journey time then improved dramatically, ushering in the era of the Enterprise service. Today, you can speed from Dublin to Belfast in just two hours (unless DART improvement works force you onto a bus for the Dublin-Drogheda stretch, in an echo of the 1852 situation).
Ironically, train passengers don't get a good view of this wonderful bridge (it's the one you cross just north of Drogheda station). For that, you need to go down to the southern banks of the Boyne estuary. There you will see that the elegant 155-metre central lattice section consists of three spans, and that there are a further 15 masonry arches, bringing the full length of the bridge to 540 metres.
Alternatively, or in additon, you could buy one of the commemorative stamps just issued by An Post, or visit the small exhibition about the building of the bridge at the Millmount Museum, Drogheda.
Sadly, the bridge's central metal section is not the original: by the early 1930s, corrosion, coupled with the introduction of heavier trains and locomotives, meant that the old wrought iron had to be replaced with a modern steel lattice. But for my money the Boyne Railway Bridge is still a wonderful piece of engineering history.
And thanks to the elegant new M1 road crossing over the Boyne, Drogheda is now nicely bracketed by bridges.