The progress of Christianity in Ireland in the first few centuries of its establishment, and the missionary zeal of its apostles abroad, brought the Church into close union with ecclesiastical foundations in Britain and on the continent of Europe. To the connection thus established is doubtless due the marked improvement in the architecture of the early Christian churches from the primitive oratories, although in these we see an advance in certain features on the pagan clochaun. The early Churches show a further development in dressed masonry, mortar-built walls, and high pitched roof, and, in point of antiquity, they may be classed amongst the most remarkable structures of primitive Christian times now to be found in Europe. Of their usual characteristics we shall here give a brief description, referring the reader who may desire more than a general sketch to Petrie’s work, the _Ecclesiastical Architecture of Ireland_, in which the subject has been fully discussed. * * * * * [Illustration: Doorway, Church of St. Colman Mac Duach, Aran Island.] _Doorways._--The doorways are generally inclined and are covered by a horizontal lintel, or headed with a semicircular arch, springing from plain, square-edged imposts. Occasionally the arch is cut out of a single stone. At Glendalough are examples in which the lintel is surmounted by a semicircular arch, the space between being filled up with masonry. The stones generally extend the whole thickness of the wall. Few of the very early doorways exhibit any kind of decoration beyond a plain projecting band, of which there are some fine examples at Glendalough. The door appears to have been placed against the interior face of the wall, as in many instances the stones, for a distance of about three inches from the angle, have been slightly hollowed, evidently for the reception of a frame. Great blocks of stone form the lintels of some of the churches; that of St. Fechin, of Fore, Westmeath, measures 6 feet by 2 feet, and is the full thickness of the wall--3 feet. The lintel of St. Colman’s, Kilmacduagh, is nearly of the same dimensions; and the doorway of the church of the same saint within the cashel, at Kilmurvey, has a lintel 5½ feet long, 1½ feet high, and extends the full thickness of the wall--2½ feet. * * * * * [Illustration: Window, Teampull Ceanannach, or Kilcananagh, Aran.] _Windows._--These are invariably small, and, with one or two exceptions, splay internally. They are headed, generally, with small semicircular arches, either formed of several small stones, or cut out of a single large one; but the horizontal lintel is common, as is also a triangular head. The sides of the windows, like the doorway jambs, almost invariably incline. They are rarely decorated, and then in the simplest manner, by a projecting band, similar to that occasionally found upon the early doorways, or by a small bead.