The remains of St Rule's church stand a short distance SE of the ruins of St Andrew's Cathedral in St Andrew's, Fife in eastern Scotland. This church now consists of an unusually tall and slender tower, rising to 32.5 metres, with a single surviving small rectangular chamber to its east. The evidence of the continuity of the lower walling makes clear that there was at least one further chamber to the east of that. Another chamber was clearly added in a later phase to the west of the tower, which may have replaced a smaller predecessor. The church has relatively thin walls in relation to its height, and they are built of notably fine masonry composed of large squared blocks of grey ashlar, rising from a narrow chamfered plinth course. A corbel table running along the north and south sides of the wall head of the eastern chamber continues unbroken, and at the same level, around the north, west and south walls of the tower, showing that the tower was initially exposed at that level on those three sides, and there is a similar corbel table running around the entire wall head of the tower, above which is a second, later corbel table.

The north and south flanks of the eastern chamber are each pierced by two small double-splayed arched windows. The outer faces of the window arches are cut into single block lintels, while the inner sides are cut through the coursed masonry, albeit with rather curiously devised voussoirs around the perimeter of the arch head. At the belfry stage of the tower, and resting on a string course, are paired windows to each face, the outer jambs of which are stepped as if for nook shafts, though there is no evidence that these were ever supplied, and the rebates are probably in any case too small to have received them. The belfry arches are cut through block lintels and have shallow mouldings running around them.

The most architecturally complex features of the church are three tall arches of slightly horseshoe-shaped form, one through each of the east and west walls of the tower, and one through the east wall of the chamber to its east. The arch through the east wall of the tower is the simplest of the three, and is of two orders of basically rectangular section, the outer order of the arch being slightly offset from the jambs, which had nook shafts with bell-shaped capitals below square imposts. There are no signs of disturbance around this arch, and it is evidently part of the first building campaign. Conversely, the west tower arch is clearly an insertion, since it is not coursed in with the adjacent walls, and its upper voussoirs cut the corbel table. Its outer arch order is more complex than that of its eastern counterpart, having a quirked cavetto moulding and an edge roll; it is uncertain what form its inner order took, since it is obscured by the wall that now blocks the arch. This arch was evidently inserted to serve as the opening into an enlarged nave, though it has been plausibly suggested on the masonry evidence that there may initially have been a western vestibule of some form on the site of that nave, which must presumably have been accessed through a smaller arch.

The church evidently continued in some use after being superseded by the adjacent new cathedral in 1318. Prior William de Lothian (1340-54) re-roofed it, and a door inserted in the east tower arch is associated with the arms of Prior John Hepburn (1482-1522). In 1789 the surviving fabric was consolidated by the Barons of the Exchequer at a time that the crown in Scotland was starting to take responsibility for many of the medieval cathedrals and monastic buildings.

The main features of sculptural interest are the two tower arches, the E chamber arch, and the belfry windows.

Construction is likely to have begun in the second quarter of the 12thc, but there is very little firm documentation about the early history of the site (see Comments).

The date of this building is one of the most hotly debated aspects of Scottish medieval architectural history. Some writers have ascribed the first phase of the building, the tower and eastern chamber, to Bishop Fothad II (c.1070–93), though there is nothing else in the surviving architectural record which supports the likelihood that such details and fine finish could have been achieved at so early a date in Scotland. One other possibility might be that it had been built during the episcopate of Turgot (1107–15), who had been St Margaret’s confessor, and who was aware of her devotion to the shrine at St Andrews. However, there is no documentation in specific support of that theory either. Perhaps it is more likely that the church was built in two distinct phases for Bishop Robert (c. 1123-59), on the site of one of the several earlier churches that appear to have been spread around the precinct.

In 1922 John Bilson pointed out similarities between both the mouldings and the slightly horse-shoe-shaped form of the arches inserted in the west face of the tower and the east face of the eastern compartment, and those of the west doorway of the church at Wharram-le-Street in Yorkshire. While that church is far smaller and less carefully finished than St Rule’s, this similarity is of some significance. Wharram was one of a group of churches given to Nostell Priory at a date before 1129, and Bishop Robert of St Andrews had initially been brought up from that priory to be prior of Scone in about 1120, before being translated to St Andrews in 1123–24. Taking account of the fact that one of the foundation accounts of St Andrews states that Bishop Robert enlarged the church he found, this would be consistent with his insertion of these arches as part of the process of expanding the church. This could have been either around the time of his eventual consecration in 1127, or around the time that his aim of establishing an Augustinian priory here took final shape in about 1138.

The part of the church that has been the subject of greatest debate is the arch that opens through the east wall of the eastern chamber. This appears to have been essentially the same as that through the west wall of the tower and, since the inner order is still exposed, it can be seen that it took the form of a leading shaft (in the jambs) and a roll on the face of a widely projecting rectangular section (in the arch). The caps are of chalice form with rounded imposts made from a darker stone. The relationship of this arch with the adjacent parts of the building has been confused by well-intentioned works carried out in 1789 by the Barons of the Exchequer, in the course of which the masonry on each side of the arch was re-faced. However, a drawing of the cathedral precinct by John Oliphant, of 1767, which depicts the church with some precision, shows that the removal of the side walls of whatever had stood to the east of that chamber had left vertical scarring in the walls. It also shows that the lower parts of the jambs of the arch had been robbed away, leaving wall core exposed. Much of the masonry now seen extending out from the jambs must therefore be the result of the work of 1789, and this is supported by the fact that an inscription commemorating that work is set within the new masonry. Oliphant’s view helps to explain why the two jambs now start at different heights above ground level and do not have properly formed bases; it is also evident that the wall above the arch has been almost completely rebuilt in order to repair a major fissure, with what remained of the gable removed.

Since the masonry on each side of the arch is thus evidently of the late eighteenth century, it cannot be looked to it in assessing whether the arch is primary or secondary. However, since the easternmost arch bears such close similarity to the west tower arch, it is likely that they are both secondary insertions in their existing form.