Drumagully Bridge, Burrenmore Rd, Castlerock, Co Londonderry, BT 51

Drumagully Bridge is an arched rubble masonry road bridge built around 1785 for Frederick Hervey, 4th Earl of Bristol and Bishop of Derry. It was designed by the Cork architect Michael Shanahan, who also worked on Downhill House, Mussenden Temple, and Ballyscullion Houses for the Earl Bishop.

The bridge carries a minor road over a stream at the north end of Downhill Forest. Though functional in purpose, it is also an architectural statement, with symmetrical pedestrian refuges, embellished voussoirs, and blind arches on both faces. The structure is constructed throughout of random rubble basalt, except for its voussoirs. The arch springs directly from the rocky riverbed and has a semicircular profile. The voussoirs are of dressed sandstone with alternating stones slightly lengthened and given vermiculated (worm-like textured) faces. The arch also features similarly embellished triple keystones. The base of the arch has been concreted to prevent scouring.

Both faces of the bridge curve outwards on either side of the arch to form square-cut piers, which rise to create pedestrian refuges at road level. Each curved section contains a shallow semicircular-headed blind arch. The approach walls beyond the refuges also have blind arches, but of wider segmental profile. The voussoirs of all blind arches are of roughly dressed basalt without embellishment. Three rubble stone buttresses shore up the approach wall at the north-west end. The original stone copings to the parapets have largely been replaced with concrete.

The bridge sits within woodland at the north end of Downhill Forest and is surrounded by trees on all sides. Just beyond its north-west end is a picturesque waterfall on a stream, which may have been artificially created by blasting. A public footpath into the glen leads from the south-east end of the bridge.

An 1835 Ordnance Survey Memoir describes the bridge as having one arch with a 24-foot span. The wall measures 54 feet long, 2 feet 6 inches wide and 1 foot 6 inches thick. The bridge is 16 feet 6 inches broad at the top. The memoir praises it as "of excellent architecture" and notes it was made at the expense of Bishop Hervey. The road leading to the bridge, which connects the mountain road to Newtownlimavady from the entrance to Downhill House, is 24 feet broad in the clear. Although now maintained at county expense, it was originally kept in repair by the Bishop. The bridge appears on all Ordnance Survey map editions from 1831 onwards.