Union Locks, Blaris Road, Lisburn, Co Antrim

The Union Locks comprise a staircase arrangement of four locks built in the early 1780s under the direction of canal engineer Richard Owen by the Company of Undertakers of the Lagan Navigation. They connect the navigable section of the River Lagan with the Lagan Canal, linking the Belfast-Lisburn section of the Lagan Navigation to the canal proper which extended to Lough Neagh.

The complex is aligned north-south on the right bank of the River Lagan, a short distance upstream from Moore's Bridge on the main Lisburn-Hillsborough road. It consists of four staircase locks, numbered 14 to 17 from the Belfast end, with an overall rise of 35 feet (10.6 metres). The highest lock, lock 17 at the south end, is separated from the others by a small curvilinear passing basin. The side walls of the lock chambers are constructed from a mixture of basalt and sandstone in both rubble and squared form, coped with large squared masonry blocks. The quoins of the sluice emplacements are of finely dressed sandstone blocks. In places, stonework has been replaced with brickwork, reflecting 19th and 20th century repairs. A cast-iron bollard survives halfway along lock 14 on its east side. Although all the cills survive, the sluice gates have been removed. At the northwest side of the passing basin is a small overspill channel, now disused and covered over for most of its length. The bed of the former canal can be traced south from lock 17 to Blaris Road, though it has been infilled in places. A lock keeper's house adjoins the complex southeast of the topmost lock.

The Union Locks survive unaltered save for the absence of their gates. They are of considerable architectural and historical significance as the only four-lock canal staircase in Ireland and as a key component of Ulster's pre-railway navigable waterways network. The Lagan Navigation between Belfast and Lisburn was built between 1756 and 1763, with the river made navigable from Union Bridge, Lisburn, to Moore's Bridge between 1763 and 1765. The Lagan Canal was constructed between 1782 and 1793, extending from Sprucefield to Ellis' Gut at Lough Neagh. The completion of this waterway enabled barges to travel between Belfast, Newry and Portadown approximately 50 years before railway connections linked these towns.

The Lagan Navigation and Canal proved commercially successful, particularly the Belfast-Lisburn section, which served a number of large mills. Control passed from the Company of Undertakers to the Lagan Navigation Company in 1843. The Lisburn-Lough Neagh section operated until 1947, and the waterway was officially abandoned in 1954 when the Lagan Navigation Company was dissolved and its assets transferred to the Ministry of Commerce. The Belfast-Lisburn section was abandoned in 1958. In 1963, a large drainage pipe was laid from the M1 motorway (built along the former canal bed between Sprucefield and Moira) to the top of the Union Locks, with water continuing to flow through the locks into the Lagan.

The lock complex was acquired by Hillsborough Council in 1971 from the Ministry of Agriculture, and transferred to Lisburn Borough Council following local government reorganisation in 1973. The Council carried out landscaping works in 1989 to open the complex as a public amenity, with further recent work including the erection of a new steel footbridge over the Lagan from the towpath on the County Antrim side of the river. The Union Locks were scheduled as a Historic Monument in 2003 under article 3 of the Historic Monuments & Archaeological Objects (Northern Ireland) Order 1995.