Holy Trinity Church of Ireland, Ballylesson Road, Belfast, County Down, BT8 8JU

Holy Trinity Church of Ireland is a double-height rubble stone barn church with tower, built around 1790 to designs by Dublin architect Charles Lilly, with later Gothic additions made around 1860 by the firm Welland & Gillespie. It sits prominently on the crest of a hill overlooking the rural setting of Ballylesson and Purdysburn, to the north of the junction between Purdysburn Hill and Ballylesson Road, and southeast of the Giants Ring. The listing extends to the church itself, its gates, gate pillars and surrounding walling.

The church follows a cruciform plan, with a single-storey vestry on the north elevation. The roof is pitched natural slate with clay ridge tiles, lead flashing to the valleys and partially over coping stones, and cast-aluminium rainwater goods with ogee-moulded gutters and circular downpipes. The earlier tower and nave are built of random rubble masonry, while the later transept and chancel extensions use random cut masonry laid partially to courses, with sandstone coping, quoins and surrounds. Windows are cast-iron framed, set into cut stone surrounds with large stone sills. The later windows feature set-piece geometrical tracery — a quatrefoil central light above, all embraced within a chamfered equilateral pointed arch with a red sandstone label course. Doors are timber with wrought-iron ironmongery.

The principal elevation faces west and is symmetrically arranged around a centrally placed three-stage tower in front of the original nave. To the left of the tower is a single-storey vestry built around 1820, with a further single-storey toilet added around 1980. The tower is square in plan, rising to an instepped upper section with chamfered corners and terminating in four plain pyramidal pinnacles. The front door is a replacement timber door retaining its original ironmongery, set into a recessed round-headed arch with a smooth stone surround and flanked by two yew trees. Above this are a pair of smaller round-headed arched windows with intersecting glazing bars, inset into a stone surround with a relieving arch over. A cut stone string course sits above, with a raked string course rising over it to portray a pediment, continuing up to a moulded stone cornice. The belfry stage has a blank oculus centrally placed, with a large timber-louvered round-headed arch rising to a second cornice level. The north face of the tower replicates the paired arched windows and louvered opening of the front elevation, though it has no oculus or raked string course. The south face of the tower retains the original 82-paned round-headed arched opening with sandstone surrounds and a split stone arch over at lower level, with a 25-paned oculus above. A modern clock face is located below the timber-louvered opening on this face. Directly behind the tower is the gable end of the nave.

The north elevation comprises two single-storey additions at ground level to the right, the nave projecting eastwards, and the gable end of the north transept to the left. The nave has two large Gothic windows on either side, dating from around 1860, which replaced the original round-headed arched openings — the distinctly newer stone above and below these windows makes the alteration legible. Recent restoration work revealed that the entrance from the porch to the nave also originally had a matching semicircular arched head, which remains in place but was altered to a pointed arch to correspond with the new nave windows. The ground floor window of the spire is of particular interest as it indicates how the original nave windows would have appeared.

The gabled transept has a kneeler stone and a string course intersecting a large sandstone oculus comprising recessed central cinquefoil tracery, complemented by fourteen outer quatrefoil oculi and surrounded by carved stone moulding. The quoin stones are carved to form a pilaster rising from the battering to the string course. To the right cheek of the transept are two paired cusped lattice lights with sandstone surrounds. The left cheek has a modern timber external door with sympathetic ironmongery, with short-and-long sandstone surrounds and a sandstone lintel inscribed 'MCMLXXXIX'.

The gable east elevation is abutted by the projecting chancel and has a moulded apex stone that forms part of a former chimney. The coping stones fall to a kneeler stone, with a gablet over a profiled gable shoulder. The chancel gable is symmetrically arranged, with an additional lean-to single-storey heating chamber to the right; the detailing matches that of the transept, with additional sandstone clasp buttressing to the corners. The large stained-glass window here is of plate tracery comprising three cusped colonnaded lights with a triple cinquefoil oculus above — this is a good quality stained glass window by Gibbs of London, made around 1865 and installed in the chancel by Robert Narcissus Batt in memory of his father. The south elevation matches the north elevation.

The church has a rich and well-documented history. According to F. Rankin, it was built around 1790 for the sum of £1,251 5s ½d, raised by subscription, and consecrated on 24 July 1791. The site was selected by Lord Hillsborough following the decision to build a new church for the Parish of Drumbo, which had gone almost 600 years without a place of worship. The land — one acre, one rood and thirty-one perches in the Upper Ballylesson townland — was granted by James Beers, one of the newly elected churchwardens, to the parish free in perpetuity, as recorded in vestry minutes of 23 October 1788. Charles Lilly, the Dublin architect who had carried out extensive work on the Downshire estate and at Down Cathedral, was engaged to produce the plans. His original drawings show a tower with a copper dome and a nave with arched windows and a shallow pitched roof. Although the copper dome no longer survives, it is referred to in the building accounts at a cost of £28 14s 11d, and Samuel Lewis in his Topographical Dictionary of Ireland (1837) described the building as "a handsome Grecian edifice with a lofty tower surmounted by a copper dome." During recent works to the tower, iron beams were uncovered that may have formed part of this dome. It is also likely that Lilly designed St John's Parish Church in Hilltown, built some years earlier in 1766 for Lord Hillsborough, which bears a striking resemblance to the early Drumbo plans.

The Ordnance Survey Memoirs of Ireland (1832–34 and 1837) recorded the church as follows: "In the townland of Ballylessan...dimensions 90 feet by 30, 25 seats, would contain 7 persons each. The church is pleasantly situated. The trees that surround it and ornamental tombstones gives an unusual but agreeable appearance." The Ordnance Survey map of 1834 confirms the church tower, nave and single-storey vestry. The Townland Valuations of 1828–40 valued the church at £10 18s. By the time of Griffith's Valuation in 1863, following the additions, this had risen to £23, with no further increases recorded in the Annual Revisions from 1865 to 1929. The Ordnance Survey map of 1901 shows the church in its current footprint, captioned 'Holy Trinity'.

The Ecclesiastical Commissioners selected Drumbo Parish for enlargement as early as 1855. Thomas Gray and James Skelton Bell were tasked with collecting subscriptions and arranging the works. The additional chancel and south transept, designed by Welland & Gillespie, were completed and opened for Divine Service on Good Friday, 3 April 1863, at a cost of £450. The north transept was added a year later, funded by Robert Batt and Mrs Caldwell.

In 1874, W. J. Watson, architect from Newry, oversaw the replacement of the original roof with one set at a much steeper pitch — the profile of the original shallower roof remains visible on the exterior gable at the east end. At the same time, the original box pews were removed and replaced with the present pitch pine pews, and the original nave windows shown on Lilly's drawings were replaced with the enlarged Gothic pointed arch windows. Local knowledge, recently confirmed during repair work, also records that the string courses at high level are upturned trimmed headstones repurposed from the graveyard.

During recent repair works to the plaster of the chancel, brick arches were revealed on either side. As there is no corresponding door to the exterior, local knowledge suggests that Robert Narcissus Batt intended these niches as memorials to himself and his wife.

In 1981, Stephen Dykes Bower — one of the leading ecclesiastical architects of the 20th century, who also advised on St Mark's, Dundela — was employed to survey the church and advise on lighting. This resulted in the addition of chandelier lighting, the wiring of the original wall light brackets, and the red walls in the sanctuary.

During the 20th century, the only additions to the church were the single-storey toilet built around 1980 adjoining the vestry on the north elevation, and the external door to the left of the chancel dated 1989 by the Roman numerals inscribed over it. In 2004, major restorative work to the internal plasterwork and roof was carried out, at which time the slates were cleaned, insulation was installed, and the slates replaced.

The current font was removed from Christ Church in Belfast following its deconsecration in 1994 and installed in the north transept. A memorial tablet to Michael Thomas Sadler, who died in 1835, was also transferred from Christ Church; although he worshipped there, he is buried at Drumbo in a grave surrounded by iron railings on the right-hand side of the path leaving the church.

The church is sited at the top of a hill, reached by a short steep incline through the associated graveyard, which encloses all sides of the church and is densely vegetated at the perimeter. From a distance, the church tower is visible above the tree line. The entrance is marked by two large square-cut stone pillars with carved sandstone cornices supporting a pair of heavy cast-iron gates, with a random masonry wall running the full length of the south side of the site along Ballylesson Road and rising on both sides to meet the pillars.