A railway viaduct built by the Dublin and Drogheda Railway to cross the Broadmeadows Estuary near Malahide station in Co. Dublin.
The first viaduct, built in 1843/4, combined eleven 52 ft timber spans with an embankment. John Macneill was the Engineer.
The obstruction to the incoming and outgoing tidal flow caused a very powerful current to rush through, the scour reducing the security of the piles and causing the bridge to settle. Rock was repeatedly dumped to protect the piers, eventually forming a rock-filled weir.
The bridge suffered serious decay, and in 1859 the railway company's engineer, Marcus Harty, was ordered to prepare plans for reconstruction.
The main girders were of wrought iron lattice construction. Instead of being painted as originally specified, the girders were immersed in a bath of hot coal tar at the works. A cast iron tank was erected, 53ft. long, 2ft. 6in. wide, and 5ft. deep. Under one end was a small furnace, with the flue running under and all round the tank to a chimney at the other end. An overhead travelling crane served the tank.
William Anderson presented a Paper to the I.C.E. in 1862 describing the design and construction, and this was reproduced in two issues of The Engineer, referenced below. Anderson emphasised that while he was the contractor for the ironwork, he had nothing to do with the design and execution of the works, which he credited entirely to Marcus Harty.
As part of the 1860s reconstruction, new masonry piers were constructed on the weir. The decks have since been replaced but the structure retained its form with masonry piers on the weir.
At some point the iron girders were replaced by concrete beams.
In 2009 No. 4 pier collapsed, bringing down the two spans bearing on it.