Yeah, I messed up a link update. Should be fixed now.
The Android version on the MEGA link should also work now - I tested it myself on an Android device and it was OK.
At their height in the days of the early Roman Republic and late Greek antiquity, Celtic peoples (which is a very broad term) covered South Eastern and Central Europe (minus Germany and Scandinavia), as well as modern France, Spain and the British Isles. So a lot of the land was actually very rich for farming and grazing. Before their colonization by the English, the Irish were a very well-fed people, mainly because their land was excellent for cattle grazing, and from that you get meat and milk.
A feature of Irish mythology that appears often (especially in the Ulster Cycle) is wealth measured by the size of cattle herds. Great battles are also fought on the pre-text of cattle raids. Ireland's greatest epic story is basically a cattle raid (the Táin Bó Cúailnge). So we can imagine Celtic Ireland as being a place where different tribes and clans lived around the earthen hill forts of their chiefs and they raided each other.