An aqueduct is an engineered structure designed to carry a body of water over some other feature. Whilst primarily used in canals, rivers can be diverted into aqueducts where diversion of the river is not feasible.
The Grand Canal spans the River Barrow in Monasterevin, Co. Kildare by means of an aqueduct. Also on this line of canal, the Leinster Aqueduct near Sallins carries the canal over the River Liffey. This saved the canal from having to lock down into the river and lock back up on the other side of the Liffey to continue its journey.
The building of the railway network in Ireland resulted in a small number of streams being diverted into aqueducts over railway cuttings, such as at Hillsborough, Co. Down and at Mossley West station in Co. Antrim, where Archibald’s Aqueduct spans the railway line.