One of the peculiar things about Irish medieval history is that, due to the texts which survived, you can read at length about the precise details of laws concerning the trespasses of people, animals, and even bees, but when it comes to accounts of celebrations, they’re pretty thin on the ground.
And Christmas wasn’t as important a celebration in early medieval Ireland as it would become in later years - the Christians of the time were much more interested in Easter, which was the subject of much debate around exactly when to celebrate it. A Irish scholar called Cummian was one of the foremost authorities on this in the seventh century, and his influence can be seen in later calculations all over Europe. (EMI, p. 201)
We do know from a number of sources, though, that feasting and drinking have been features of an Irish Christmas from the very earliest days. It seems, for example, that getting drunk then was much more allowable than otherwise, even for monks. The Paenitentiale Bigotianum, a set of rules for penance probably composed and certainly used in Ireland sometime between the seventh and ninth centuries, has a section that reads, in translation:
“If a monk vomits because of drunkenness, he shall do penance for thirty days; if [he is] a priest or deacon, he shall do penance for forty days, but if he does so because of… after drinking the joy of Christmas or Easter or the commemoration of any of the saints and on those occasions takes no more than what has been decreed by the seniors, it does not matter.” (Hospitality in Medieval Ireland, p. 189)
So in other words, as long as you could talk the abbot into saying you could keep drinking, you could keep on going.
A little later on, we can see among the exploits of Maelseachlainn, an Uí Néill “high king”, who seems from an account in the Annals of the Four Masters to have been quite a conqueror:
“The battle of Athcliath was gained over the foreigners by Maelseachlainn, in which many of the foreigners were slain by him. And he afterwards laid siege to the fortress for the space of twenty nights, so that they drank no water during this time but the brine. At length they gave him his own full demand while he should be king, and an ounce of gold for every garden, to be paid on Christmas night, for ever.” (Annals of the Four Masters, M988.11)
Athcliath is Dublin, and the foreigners were the Vikings who had settled there. One can imagine that the tribute of an ounce of gold per garden made the Christmases of Maelseachalainn and his descendants merry indeed, and Dáibhí O Cróinín notes in Early Medieval Ireland that “[f]or the next century and a half, Irish kings preferred to see the ‘foreigners’ of Dublin as a source of wealth and tribute” (p. 260)
Later medieval rulers claimed special privileges from their sub-chiefs. Catherine Marie O’Sullivan notes in her excellent book, Hospitality in Medieval Ireland that “A late medieval tract listing the privileges of Mac Mathghamhna of Monaghan shows three hereditary sub-chiefs fo the Oirghíalla owing him two night’s refection […] in the winter […] after Christmas” (p. 52), refection being the duty to play host to one’s lord at certain times, which could be a very expensive proposition.
O’Sullivan also says that in 1397, a Catalonian pilgrim called Ramon de Perellós was invited by Niall Ó Néill, then the king of Ulster, to spend Christmas in his court. He described much of what happened, not just with reference to the good and the great, but also the common people:
“There was a great number of poor people following him and I saw the king giving the great alms of ox-meat … On Christmas Day, as my interpreters and others who could speak Latin told me, the king held a great court. Nevertheless, his table was of rushes spread out on the ground while nearby they placed delicate grass for him to wipe his mouth. They used to carry the meat to him on poles, in the same way as they carry semals, in this country… The king received me very well and he sent me an ox and his cook to prepare it. In all his court there was no milk to drink nor bread nor wine, but as a great gift he sent me two cakes as thin as wafers and as pliable as raw dough. They were made of oats and of earth, and they were as black as coal, but very tasty” (p. 193)
As a food historian, I am very curious as to to what these cakes might have been, although I don’t entirely trust Ramon’s recipe of oats and earth. Some kind of oaten pancake, perhaps?
There’s an account, too, in the Geinealach Chorcha Laidhe, of a celebration in Cork in 1413 involving dance, drink, and the singing of a carol, only to have the party interrupted rudely by the mayor of Waterford arriving to take the chieftain prisoner. (p. 194)
And then another account by Tadgh Dall Ó hUiguinn says that at a 16th century Christmas celebration held by another Ó Néill king, “even were I as the shoulder of any man I could not hear him because of the strains of music from the citadel. Ere we had arrived beside it, it seemed to me that the brilliance of its many-surfaced goblets, and the fragrant odour of its banquet ales were of themselves a sufficient enjoyment” (p. 189)
So while we may not be able to pin down any exact traditions, we can certainly say that eating, drinking, and making merry at Christmas are supported by long tradition - and exempt from penance!