Leuchars is a small town in the north-east of Fife, Scotland, situated 6 miles north-west of St Andrews. The plan of the medieval church of St Athernase and Bonocus is only partly known, since no more than the square chancel and eastern apse survive. It is uncertain if there was ever a tower at the west end of the nave, though, bearing in mind that churches of comparable date and quality such as Dalmeny and Tyninghame did have west towers, it might be thought unusual for such an ambitious church as Leuchars not to have had one.

The chancel was walled off from the nave at some date after the Reformation, apparently leaving little visible evidence of the fine arch that had opened into it. An octagonal two-stage domed bell tower was raised over the apse that can probably be attributed to John Douglas, who is known to have worked on it in 1744, but the line of the earlier apse roof is still visible against the east gable wall of the chancel. The nave was extensively remodelled for parochial worship on a number of occasions, and there are recorded works in 1812-14 by Robert Balfour. At some stage a lateral north aisle was added.

The nave was entirely rebuilt to an elongated rectangular plan and in a mildly Romanesque idiom in 1857-8 by John Milne. Its show front, to the south, has a central gabled salient with a door covered by a later porch; that salient is flanked symmetrically by pairs of windows and by a doorway towards each end, that to the east being now blocked. On the less visible north side, considerable extents of cubical masonry suggest that Romanesque fabric has been re-cycled. Milne also carried out some restoration works on the chancel and apse.

A more scholarly restoration was carried out by Reginald Fairle in 1914, who reopened the chancel arch towards the nave. Within the re-opened arch he placed a timber screen, but this was relocated to the vestibule to form a baptistery area in 1935. Fairlie had also proposed shortening the nave of the 1850s, while doubling its width towards the north and adding a western tower and narthex.

The Romanesque chancel and apse are remarkable for their extraordinarily lavish external decoration, with two levels of blind arcading carried on decorative string courses that run around both parts. At the lower level of the chancel flanks the arcading is intersecting and carried on paired en délit shafts with cushion or scalloped caps. At the upper level of the chancel the arcading is simple, and is carried on en délit shafts flanking pilaster-like projections; the upper arches have continuous mouldings to the inner order and a cable moulding to the outer.

The lower level of the apse has simple arcading that is carried on engaged pairs of shafts separated by a spur, with chevron decoration to the arches. The apse rises to a lower height than the chancel, and the simple arcading to its upper level is carried on similar supports to those of the chancel, though the arches have chevron to the inner order and multiple billet to the outer. There is greater variety to the capitals of the upper apse arcading, with several of volute form. The wall-head around both chancel and apse has a decorative corbel table with grotesque human and animal heads.

Enclosed within the upper arcading around chancel and apse, there are two small-rounded windows to the south flank of the chancel and one on the north, while the apse has three such windows. It appears, however, that in their present form they date from John Milne’s restoration of 1857-8, and that they replace ‘two square windows with a single stone mullion’ in the south chancel wall and one in the apse. It is likely, however, that the original windows were of this form.

On the north side there is evidence that the Romanesque nave was, as might be expected, slightly wider than the chancel, though it did not extend so far to the north as the nave of 1857-8. The evidence for this is seen in the survival of its base course below the east face of the north-east corner of the mid-nineteenth-century nave. There is also above it a corresponding section of decorated string course, at a level corresponding to mid-height of the upper level of blind arcading on the adjacent chancel. The evidence has been somewhat confused by the way in which that string course has been extended by reset lengths of string course with the same moulding along the whole of the east nave wall and back along the eastern part of its north wall. But there can be little doubt that the base course provides a firm indicator of the width of the nave on the north side, because it can be seen that it returns towards the west.

Internally, it is clearer than on the exterior that the chancel has been heavily restored, and there must be some doubt over the extent to which there was any basis for the form of the restored rear-arches to the two windows in the south wall and the one in the north. The rear-arches of the apse windows, however, appear to be more likely to reflect their original form. Their chevron-decorated arches are carried by en délit shafts that rise from a string course.

Rising from that same string course, above grotesque head corbels, are wall shafts that support the ribs of the vault, which have triple-rolls to their soffits. The ribbed part of the vault is confined to the semi-circular eastern part of the apse, and there is a short section of barrel vault to the western part. There may have been some restoration of the vault when Reginald Fairlie removed an arch that had been inserted to support the tower over the apse. There is no evidence that the chancel has been vaulted.

The chancel and apse arches are the finest features of the interior. The responds in each case have a leading half-shaft on the face of a pilaster, which is itself flanked by three-quarter nook-shafts, and the caps are of cushion or scalloped form. The chancel arch has an inner order with triple soffit rolls and simple chevron to the leading face, while the outer order has continuous mouldings and there is a chip-carved hood mould. The apse arch is more richly treated, with two chevron-decorated orders and a billet-carved hood mould towards the chancel.

Leuchars was granted to St Andrews Cathedral Priory, at a date between 1172 and 1187, by Ness, son of William, whose name could suggest that he was the offspring of a marriage between a native mother and an incomer of French origin. Despite that grant, patronage of the church was to be contested for a number of decades. On the stylistic evidence of the surviving parts, it is perhaps most likely that the earliest portions of the church were built no later than the central decades of the twelfth century, and thus some decades before the grant to St Andrews. There was a dedication by Bishop David de Bernham on 4 September 1244, but that is unlikely to be of any significance for the fabric, since de Bernham dedicated a high proportion of the churches in his diocese, evidently to ensure that they were appropriately prepared for worship.

There is an ongoing debate over the location of the principal altar in the parish churches of the mid-twelfth century. It is frequently suggested that, where there is an apse, that apse was not intended to house the altar, so much as to act as a back-drop to it, and at Dalmeny, for example, where the chancel arch is more richly treated than the apse arch, it may indeed be that the altar was within the chancel. At Leuchars, however, a number of factors might suggest that the altar was within the apse: the apse arch is treated more richly than the chancel arch, suggesting it marked the entrance to a more important part; the chancel is unvaulted; and the elongated plan of the apse is internally emphasised by the section of barrel vault over its western part. This is not in itself conclusive for the location of the altar, though it is suggestive.

It has been plausibly suggested that the presence of some of the same masons’ marks as are found at Dunfermline Abbey indicates that a number of masons were involved at the two buildings. While it is by no means certain that a mason would use the same mark at different buildings on which he was involved, the presence at Leuchars of masons from Dunfermline, some of whom may have worked previously at Durham, would be a satisfactory way of explaining both the decorative repertory and the quality of much of the work.