One of very few surviving objects known to have been the personal property of an Irish king, the Kavanagh Charter Horn is a ceremonial drinking horn of elephant ivory dating from the early 12th century. The brass mountings were added in the 15th century. It is the only known piece of Irish regalia to survive Medieval Ireland. The Kavangh clan’s bloodline ruled the kingdom of Leinster. The family retained possession of the horn until they decided to donate it to the National Museum of Ireland.
Drinking horns are mentioned in many Irish chronicles. Many were very valuable and passed from generation to generation. They were valuable not only because of their material makeup, but because of the symbolic value.
I’d assume that most of the drinks horns like these would’ve held different alcoholic beverages from the time, primarily beer and wine. Monks brewed virtually all beer of good quality until the twelfth century. Around the thirteenth century, hops (which both flavors and preserves) became a common ingredient in some beers, especially in northern Europe. Ale, often a thick and nutritious soupy beverage, soured quickly and was made for local consumption. (http://www2.potsdam.edu/hansondj/Controversies/1114796842.html#.UuTuGRZ6gmI)
I guess the pub culture of Ireland goes way back!