” Called in Latin casula planeta or pænula, and in early Gallic sources amphibalus, the principal and most conspicuous Mass vestment, covering all the rest. Nearly all ecclesiologists are now agreed that liturgical costume was simply an adaptation of the secular attire commonly worn throughout the Roman Empire in the early Christian centuries.
Of the chasuble as now in common usage in the Western Church two principal types appear, which may for convenience be called the Roman and the French. The Roman is about 46 inches deep at the back and 30 inches wide. It is ornamented with orphreys forming a pillar behind and a tall cross in front, while the aperture for the neck is long and tapers downwards. The French type, also common in Germany and in a more debased form in Spain, is less ample and often artificially stiffened. It has a cross on the back and a pillar in front. In medieval chasubles these orphrey crosses often assume a Y form, and the crosses themselves seem really to have originated less from any symbolical purpose than from sartorial reasons connected with the cut and adjustment.
It consisted of a square or circular piece of cloth in the centre of which a hole was made; through this the head was passed. With the arms hanging down, this rude garment covered the whole figure. It was like a little house (casula). This derivation is curiously illustrated in the prophetic utterance of Druidical origin preserved in Muirchu’s “Life of St. Patrick”, almost the oldest allusion to the chasuble and crosier which we possess. Before St. Patrick’s coming to Ireland the Druids were supposed to have circulated this oracle:
Adze-head [this is an allusion to the peculiar Irish form of tonsure] will come with a crook-head staff; in his house head-holed [in suâ domu capiti perforatâ, i.e. chasuble] he will chant impiety from his table [i.e. the altar]; from the front [i.e. the eastern] part of his house all his household [attendant clerics] will respond, ‘So be it! So be it!’
The fact that at an early date the word casal established itself in the Celtic language, and that St. Patrick’s casal in particular became famous, makes the allusion of the “house head-holed” almost certain.” –From the Catholic Encyclopedia
And as always, the Pope!