The Boyne Viaduct, a 30m (98ft) high railway bridge, or viaduct, that crosses the River Boyne in Drogheda, carrying the main Dublin–Belfast railway line.

It was the seventh bridge of its kind in the world when built and considered one of the wonders of the age. Designed by the Irish civil engineer Sir John MacNeill and built during the 1850s, completed 1855, the bridge is located near a tight curve, which necessitates the slowing of Iarnród Éireann trains and the joint Iarnród Éireann and Northern Ireland Railways Enterprise services before they approach. Prior to its construction railway passengers had to make their way, through the town, from the stations on either side of the river. The first train, weighing 75 tonnes, made its way across the river on May 11, 1853.

The viaduct comprises twelve stone arches on south side, and a further three on the north. The central lattice truss bridge was originally made of three iron spans that were wide enough to carry two tracks. When the bridge was refurbished in the 1930s, new steel girders replacing the ironworks were constructed inside the original bridge before the iron structure was removed. This allowed trains to continue running throughout the renewal process, however the new bridge was no longer wide enough to carry two tracks. The northbound and southbound tracks were interlaced so that one rail lay between the tracks in the opposite direction, as points and a single track would have required a signal cabin on the north side of the viaduct. When the tracks were relaid in the 1990s, the interlaced tracks were replaced with a single track over the viaduct and points at each side.