None but the theologian would essay a valuation of the relative orthodoxy of converted and unconverted, but the archæologist must hold no uncertain opinion as to their merits. The unification, so far as it has gone, of the two ancient Churches with Rome is an unmitigated misfortune. The Chaldæans and the Syrians, instigated perhaps by their pastors, have been so eager to obliterate the memory of their former heterodoxy that they have effaced with an unsparing hand all, or nearly all, Syriac inscriptions older than the date of their regeneration, and in Môṣul it is rare to find any written stone earlier than the end of the seventeenth century. This is the more provoking as several of the churches are of great architectural interest, and it is much to be regretted that the epigraphic record of their history should not have been preserved. So far as I could judge, the oldest parts of the oldest churches may probably be dated in the twelfth or thirteenth centuries. All have been considerably remodelled; some were entirely rebuilt after the siege of Môṣul by Nâḍir Shah in 1743 and others have been rebuilt in recent years.[145] Moreover there are several which would seem to have been first founded as late as the eighteenth century. But whatever may be their date, they all exhibit the same simple plan, a plan which I believe to be essentially Mesopotamian and more ancient by many centuries than the existing churches. It is that of the barn church, the church with two aisles and a nave, covered by parallel barrel vaults so equal in height as not to admit of a clerestorey.[146] The nave and aisles are invariably cut off from the sanctuary by a wall--it is too substantial to be called an iconostasis--broken by three large doors. This complete separation is not typical of primitive ecclesiastical architecture; it results, as a rule, from a development of the ritual; but it appears to be here a part of the original plan. The sanctuary is almost invariably divided into three parts, corresponding to the nave and aisles, and, as a rule, the central altar is covered by a dome set upon squinch arches. The church of Mâr Ahudânî will serve as a typical example (Fig 168); it is now in the hands of the Chaldæans. A flight of steps leads down to it from the street, and the fact that it lies so far below the modern level is one of the indications of its antiquity. The stair opens into a small atrium with a cloister to east and west. The church is to the south of the atrium and there is no means of approach to it from any other side. The present atrium is comparatively modern and the church shows many signs of reconstruction and repair. The doorway from the nave to the sanctuary is richly decorated with Arabic inscriptions, with [Illustration: FIG. 168.--MÂR AHUDÂNÎ.]