Roman Temple, "Arthur's O'on", Stenhouse (Site). This remarkable building, which survived until 1743, was situated on the North side of the road from Carron to Stenhousemuir, opposite the N.W. corner of Carron Iron Works and just inside the grounds of Stenhouse. Its date and purpose have been the object of much speculation in the past, and the present account is a summary of a detailed study which has recently been published by one of the Commission's officers. The O'on was built of dressed freestone and in appearance was shaped like a beehive, being circular on plan with a domed roof: the internal diameter was 19 ft. 6 in. and the original height over 22 ft. The wall was about 4 ft. thick at the base but narrowed as it rose, and the dome was constructed of overlapping horizontal courses with their faces dressed to the proper curve. An opening in the centre of the vault, which measured 11 ft. 6 in. across by the 18th century, was probably not an original feature, but may have been caused initially by a finial breaking off, and subsequently enlarged by the collapse or removal of some of the stones. The doorway, a round-arched opening measuring about 9 ft. in height and 5 ft. in width, was situated in the E. side, and immediately above it there was a nearly square window. Round the interior of the building there were two string-courses at distances of 4 ft. and 6 ft. respectively above the paved stone floor, and in several places, notably over the door, there may have been much weathered carvings in which eagles and the goddess Victory are said to have been represented.

Although the design of the dome has no precise parallels in Roman architecture, the identification of the O'on as a Roman temple or shrine can hardly be doubted in view of its isolated position 2 miles from the nearest Roman fort or road, the fact that it faced E. in accordance with ritual practice, and the discovery in a chink of the masonry of a brass finger which had presumably been torn from a cult statue. It may be thought, however, that a structure of this kind, which bears the unmistakable stamp of legionary workmanship, is too elaborate for a purely local or private sanctuary; and since it appears to have been deliberately sited to be visible from the Antonine Wall, it seems possible that the O'on was primarily a triumphal monument, or tropaeum, erected to commemorate a victory, presumably the victory that was crowned by the construction of the new frontier line between the Forth and Clyde. Such at least is the traditional explanation recorded in a gloss in the Historia Brittonum, and it is worth recalling that on Hadrian's Wall a war-memorial was also apparently set up a short distance in advance of the barrier.