Before leaving the banks of the Carron we must call the reader's attention to that singular specimen of Roman architecture which once stood by its waters, near the place now occupied by the Carron Ironworks (it stood upon a slight rising ground, sloping to the S. or S. by E. about 300 feet to the north of the point which is now the N.W. corner of these works), and which was familiarly known by the name of 'Arthur's O'on:' we have no account of any similar remains having ever existed in North Britain, and as it occupied a position so near to that of the ancient Camelon, it may not improperly be taken notice of here. This building was of a circular form, its shape in some measure resembling that of a common bee-hive. It measured at the base from twenty-nine to thirty yards in circumference, and continued of the same dimensions to the height of eight feet, from which point it converged gradually inwards in its ascent, till, at an elevation of twenty-two feet, the walls terminated in a circle, leaving in the top of the dome a round opening twelve feet in diameter. On its western side was an arched doorway, nine feet in extreme height, and above it an aperture resembling a window, of a slightly triangular form, three feet in height, and averaging nearly the same in width. The whole was formed of hewn freestone, laid in regular horizontal courses, the first of them resting upon a thick massive basement of the same material, which, to follow out the simile, represented with curious fidelity the common circular board on which the cottage hive is usually placed. The interior of the structure corresponded with its general appearance from without; the only difference being in the concavity of the shape and in its having two projecting stone cornices round its interior surface, the one at a height of four and the other of six feet from the ground. The style of the workmanship was singularly perfect, and showed an intimate acquaintance with masonic art. No cement of any description had been made use of in its construction, yet the stones were so accurately joined together, that even the difficult process of forming so diminutive a cupola by the concentration of horizontal courses, was accomplished there in the most skilful and enduring manner.

From the days of Nennius, (he is supposed to have flourished in the 7th century and to have been the Abbot of Bangor about the year 620 Bishop Nicholson, however, assigns him a later era by 200 years), down to those of Horsley, 'Arthur's O'on' seems to have commanded the attention of almost all who laid any claim to the merits of antiquarian research. It was examined, measured, and remeasured, again and again, even to its minutest details, with a care and devotion carried, many would say, somewhat to excess, curious as the subject really was. The name of its builder, the cause of its erection, and the purpose for which it had been intended, have each, in turn, given scope to a good deal of learned disquisition, without effectually clearing away the mystery which hangs over the history of that singular structure.

Nennius is the earliest author who takes notice of it: he gives a brief description of the building, and asserts, without hesitation, that it was erected by the usurper Carausius, who assumed the purple in Britain in the year 284. He likewise mentions that a triumphal arch was built near it, in honour of the same individual, and that his imperial name had descended to posterity, retained, in some degree in that of the 'Carron'. Johannes Major, another member of the Church, tells us that it was known in his time by the name of 'Julius's Hoff.' Hector Boece ascribes the structure to Vespasian, seriously observing that he placed it there in honour of his predecessor Claudius; and that the ashes of a certain Aulus Plautius, who died at Camelon, which he calls Camulodunum, were afterwards buried within it. All those statements may be regarded as mere fables. Nennius is the only one whose account makes the slightest approach even to probability. It is well known that neither Julius Caesar nor Vespasian ever visited Scotland; and it is ridiculous to suppose them to have had any connection with the construction of Arthur's O'on. Passing over, however, the speculative theories of Hector Boece, we gather from his writings some few particulars regarding the building, which are not altogether unworthy of notice. He says, for instance, that the figure of a Roman eagle had at one time been visible, chiselled upon the pavement, and that a huge stone altar stood in the interior, on which the 'Gentiles were wont to offer sacrifice;' while, in a subsequent portion of his history, he leads us to infer that many other insignia of the Romans formerly ornamented its walls: for, he states that when, for some reason unexplained, King Edward the First had made special war on our Scottish antiquities, he was only induced to spare the 'temple beside Camelon,' after the inhabitants of the neighbourhood had already destroyed all the Roman sculptures and inscriptions which existed upon it. A gentleman named Sinclair, who visited the place, in 1569, observed the traces of a row of letters above the doorway; while Sir R Sibbald says, that when he 'narrowly viewed the walls with a lighted link,' he plainly saw on their interior surface the representation of an eagle's head and the more indistinct traces of what he conceived to be a figure of Victory, with the head and part of the handle of a javelin at her side, and the following letters immediately under: I.A.M.P.M.P.T.; which he honestly declares were to him perfectly unintelligible. Combining those several accounts together, it seems very probable that the stones of Arthur's O'on, latterly so barren of the slightest index to its history, were studded of old with many a warlike device or graven line, calculated to preserve in remembrance the object of its, erection. But all these were gone, or so far obliterated as to be unintelligible, before the spirit of inquiry became directed towards them; and the antiquarian world has, in consequence, been greatly divided in opinion as to the particular purpose which the building was intended to serve, although no one appears to have had any hesitation in deducing its origin from the era of the Roman occupation.

There is much probability that Arthur's O'on had been designed for a Sacellum or minor temple of some kind or other. Its peculiar form and appearance, the manner in which it was constructed, the votive altar, and circular opening at the top, might be supposed sufficient to denote as much. The chief difficulty experienced, by those who gave their attention to the subject, was to decide, with something like certainty, on the object of its erection, or on the particular deity to whose service it was dedicated. George Buchanan entertained the opinion that it had been consecrated to the god Terminus, as standing on the limits of the Roman province. Dr Stukely thought that it might possibly have been dedicated to Romulus, the parent deity of Rome, and that it was a work of Agricola. Sibbald contended for the honour of Coelus, the son of Terra, and ascribed its origin to the piety of Severus. Gordon, with somewhat opposite views, attacks the opinion which gave it a purely devotional character, conceiving the little Temple of the Carron to have been principally made use of as a depository for the safe keeping of the legionary standards. Some have regarded it as a trophy of victory, or a memorial of peace; others as a sepulchral monument raised to the memory of some officer of rank. Every variety of conjecture which could be advanced as at all applicable to the subject, seems to have been formed on the subject of this antique remain. We must, however, leave those speculations, to find with the reader what favour they may, satisfied that the actual history of Arthur's O'on remains involved in too deep an obscurity to be in the slightest degree cleared up by any opinions which we might venture to hazard upon the question.

Were the building still in existence, we should perhaps be forgiven for dwelling a little more minutely on the subject; if only for the sake of the passing traveller, who might, in such a case, have been tempted to turn from his way, with the object of beholding the last prominent object of Roman architecture which Scotland contained; but the ancient Sacellum, which had stood for fifteen centuries by the 'dark winding Carron,' facing unshaken the rude buffets of time, spared alike by Pict and Scot, by Saxon, Norman, and Dane ; which, if what is writ be true, had beheld the passing legions of Severus, the gathering of Ossian's heroes, the adventurous march of Wallace, the fight of Bannockburn ; this venerable monument of departed ages; fell in the year 1743 before the perhaps pardonable vandalism of a Scottish proprietor, whose tastes, centred round a comparatively narrow point, could neither appreciate an interest in the past, nor make any allowance for what he regarded as the foibles of others. In his eyes, the walls of the Roman chapel were vested with no peculiar interest; and, at a time when such materials happened to be wanted, he caused the building to be pulled down, and its stones to be made use of for the construction of a river dam. This, we are told, was afterwards swept away by the current, so that, in all probability, the last remains of Arthur's O'on lie at the present day buried amid the muddy shallows of the Carron.

Various remains of antiquity have been discovered near its site, such as the stones of Querns or hand-mills, made of a species of lava resembling that now obtained from the mill-stone quarries of Andernach on the Rhine; fragments of pottery, and the vestiges of what was supposed to have been a potter's kiln, Sibbald refers to the horns of 'great cows,' and to a patera dug up beside this Roman Sacellum, as some proof of its having been a place of sacrifice; he likewise states that the traces of a broad ditch could, in his day, be seen on its northern side; which makes it sufficiently probable that a regular vallum and fosse had once surrounded the building. As before said, however, nothing remains connected with Arthur's O'on but the memory of its existence and the green bank sloping where it stood.