Above: Ruins of early Irish monastery

Many of the hatha, as indicated, placed their duns at the disposal of Patrick and his disciples. " The house of Con all brother of the king of Meath, was given up to St. Patrick on the occasion of its master’s conversion, and the church of Downpatrick at Tailtean was built upon that site. The fortress of Dun Lughaidh was also given up to St. Patrick when the lord of the country and his four brothers and father were baptised, and the church of Kilbennan was founded within its walls. The cathair or stone fortress of Aodh Fionn, son of Fearghus chieftain of Breithfne, was given up to Caillen that he might erect the monastic buildings within it; and the interior of the fortress of Muirbheach Mil, the Firbolg chief, in the island of Aran, is now occupied by the remains of the primitive cells of the first Christian converts." These royal duns were strongly built and surrounded by stout caiseals. The caiseals of the monasteries were neither so stout nor so high, being merely single walls. The doors, too, were neither so high nor so strong as those of the dun, as may be seen at Innismurray and elsewhere.
It has been held by some authors that the only difference between the cells of the periods antecedent and subsequent to the coming of the faith was that the former were circular both inside and outside whereas the latter were circular outside and quadrangular inside. Clochan na Carraige in Aran was of the first class. This is nineteen feet long inside, eight feet high, less than eight feet wide, walls four feet thick, door three feet high, two and a half feet wide on the outside, two feet on the inside. The side walls incline towards each other as they rise till they ultimately meet at the top where they are closed by a single stone. Two holes in the centre served as window and chimney.
Foreign writers have alleged also that no building implements were used in ancient Ireland. Margaret Stokes on the other hand rightly contends that the chisel was in use from the coming of the faith, at latest, and that mortar was used from the same period.    Flann Mainistreach refers to three builders, Caomhan, Cruithneach and Luchraidh, as in the company of Patrick. Daimhliag Chianain, now Duleek, is reputed the first stone church built in Ireland, and Cianan after whom it is named, died in 400. Gallarus in Corca Dhuibhne may be equally ancient. It is the most beautiful and best preserved church of its period in these countries. Its length is 23 feet, height 16, width 10. The door, in its western end, is 5| feet high ; the stone roof a development of the strong side walls, drawing nearer, somewhat in the form of an arch, as they rise, until closed at the top by a single stone : to shed moisture, stones, instead of being laid horizontally, slope slightly outward. Tombstones lying around the church have ogham inscriptions. Beside is Cill Maelcheadair, another very ancient church, and connected with it an Abecedarium stone, with a very early Irish alphabet.
The house of St. Fionan Cam in Loch Luighdheach near Waterville, Kerry, is a cyclopean structure, circular outside, quadrangular inside, 16 feet long, 15 feet wide, and the walls 7 feet thick at the base. Another house of the period is that of Kelts in Meath. It is of dressed stone and mortar, and is estimated to have been built between the middle and end of the sixth century.
At the same time was erected Dairbhile’s church at Erris. It is 40 feet long, 16 feet wide, and built of polygonal stones of local granite. On the east side, it has a small window, semicircular at the top. The door on the west side is also semicircular at the top. Door and window are each covered with a single stone shaped like an arch. Though striving after the arch, it is evident that native builders were not yet familiar with its principle. But they developed it steadily, as did the Greeks and other peoples.

Above: Early Irish architecture

A hundred years after the Christian era the four great fortresses of Ireland were erected or enlarged by Tuathal Teachtmhar at Tlachtgha, Taillte, Teamhair and Uisneach. Tara was extended at the hands of many successive kings. Though the Fiana favoured the outdoor life, all the great kings of our race had their architects. The names of some, indeed, are preserved amongst those of the world’s great builders, notably Car, builder of Cashel; Righriu and Garb-ban, builders of Aileach ; Bole, builder of Cruachan ; Troigleathan, of Tara ;   Balor, of Breise ;   and Criceal of Ailinn.
The house of the flaith was called a lios. A lios surrounded by a clay fence, in the shelter of which was a pen for cattle, was called a rath. A wall of uncemented stones surrounding the lios was a caiseal;   some  of the caiseals exceeded 220 feet across.    The dun was the residence  of  the  king.   A dun, on a point, headland or promontory, connected by a narrow neck with the adjoining land, was protected by a high wall drawn across the neck.    A dun, with a stone wall inside, was called a cathair.    Most of the cathairs, circular in shape, had platforms on the inside, connected by alternating flights of steps, and reaching almost to the top of the main wall:   from these the defenders were able to fling volleys of stones or other convenient missiles.    As in Greece, special compartments, over the front of the house, were set apart for the women.    Other classes of buildings were the brugh, both, bothan and so on.
Religious buildings included the daimhliag,  temple, cell, reilg, eaglais, cro, clochar, monastery.    With the spread of the faith, many duns were converted into churches.    Kings and chieftains on their conversion offered their duns to God, and cells and oratories soon arose within them.    Some confusion thus arose in the naming of them, as in the case of Rathboth, now Raphoe.    So,  too, it would be difficult to say now whether buildings like Cathair na Mactireach in Corca Dhuibhne were originally duns or churches.    Many cells are there enclosed, and the edges of the stones sometimes protrude beyond the door wall to strengthen it.    The doors, moreover, are narrower on the inside.    Though the measurements of St. Patrick’s fearta near Ard Macha were, by the Apostle’s own advice, caiseal 140 feet,  daimhliag   27 feet, kitchen 17 feet,  oratory 7 feet,  and these were the usual dimensions of the principal churches of the time, the early Irish monks, like those of the East, went into the wilderness and spent their lives in solitary contemplation of the goodness of God.    Some of them lived in caves and cells ; and in the east of Ireland the cells, made of wood, soon perished. Examples are afforded by Mobhi’s cells at Glasnevin when visited by Colm  Cille,  and by Brigid’s house at Kildare, which was made of wattles.    Stone cells,  accommodating at the outset a single person, were the order in the south and west, where, unlike the east, they still survive, and contrast very unfavourably with the Pagan architecture which preceded them. But disparities like these are true of all periods and of all countries, true of ancient Athens as of the modern capital of Greece.