Spencer's Bridge, Hillsborough Road, Moira, Craigavon, Co Armagh

Spencer's Bridge is a triple-span masonry arch bridge carrying a secondary road between Moira and Hillsborough over the floodplain of the River Lagan in County Armagh. Although a causeway has likely existed at this location since at least the mid-18th century, the bridge itself was probably rebuilt at least once during the first half of the 19th century.

The bridge is constructed of random rubble masonry throughout, except for the cutwaters and arch voussoirs. The cutwaters have a triangular profile and step up at both ends of the piers to just above arch spring level. They are built of dressed sandstone blocks laid to regular courses and continue upward to the tops of the parapets as shallow rectangular basalt rubble pilasters. The three arches are of equal size with a three-centred (semi-elliptical) profile. Their voussoirs are of vee-jointed cut sandstone with slightly projecting keystones. The arch soffits have been rendered with cement, though random rubble is visible in places. Two tie rods per arch hold the sides of the bridge together.

The downstream (north) elevation is identical to the upstream (south) elevation except for a lagged water pipe that runs across above crown level. This pipe sits on a rolled steel joist supported on crude mass concrete columns rising from the sandstone cutwaters. The carriageway has a slight hump and carries two lanes. The parapets have drainage slits at road level and are coped with chunky undressed stones. Inserted into the upstream parapet directly over the crown of the middle arch is a finely dressed granite post with a square cross-section and rounded top, inscribed with the date '1843'. Immediately above this date is a small cast-iron plaque bearing a coronet and the letter 'D', denoting Downshire, the principal land-owning family in the area.

The long approach roads are walled on either side with random rubble masonry and have been strengthened at their bridge ends with random rubble buttresses; the eastern buttress is relatively recent. A small segmental-headed flood arch with cut sandstone voussoirs is visible on the eastern approach. A similarly sized flood arch is visible on the north side of the western approach, though it is blocked or obscured by vegetation on the upstream side. This latter arch has split stone voussoirs and appears to be of earlier date. According to the 1837 Ordnance Survey Memoir, there were five flood arches in total, though three were not observed during survey and have probably been buried or hidden by vegetation.

The bridge takes its name from the Spencer family, landowners in the Trummery district a mile south of the bridge. It was cited as Inisloughban Bridge on Oliver Sloane's 1739 map of County Down, but both Walter Harris' 1744 map and Taylor & Skinner's 1777 map refer to it as Spencer's Bridge, a name that persists on subsequent Ordnance Survey maps from 1834 onwards. The 1837 Ordnance Survey Memoir for Magheramesk Parish records the bridge's dimensions: centre arch span of 22 feet, outer arch spans of 21 feet each, average road breadth of 21 feet 6 inches, average parapet height of 4 feet, parapet thickness of 1 foot 6 inches, and total parapet length of 355 yards on either side of the road, with the bridge itself measuring 30 yards in length. The memoir also documents the five flood arches: three on the County Down side with spans of 12 feet, 7 feet, and 7 feet respectively, and two on the County Antrim side each with a span of 10 feet. It describes the large bridge arches as "faced with cut freestone" while "the remainder of the work, including the parapets, is built of quarry and land stones."

The precise date of the bridge is uncertain. The fine quality of its arch voussoirs would accord with early or mid-19th century construction. The arch voussoirs are described in the 1837 memoir as faced with cut freestone, suggesting they were either rebuilt in 1843 or that the date stone over the middle arch marks when the post was positioned, possibly as a boundary marker of that date rather than a record of the bridge's reconstruction. The crude flood arch in the western approach would not be out of place in an 18th-century context. Historical records indicate that the bridge was said to be erected at the expense of both counties through which it passes, though no accurate record of its construction cost, date, or engineer survives.

Though its character is somewhat marred by the crude manner in which the water pipe is carried across it, the bridge retains considerable architectural interest through the quality of its arches and their contrast with the remaining rubble stonework. As an impressive landscape feature when viewed from afar and a good example of a causeway bridge across the Lagan's wide floodplain, it forms an important visual element in the landscape. Its association with the Downshire Estate further enhances its local historical significance.