A span of 10,000 years spreads between now and the first possibility of settlement on the island of Eire, then swept clean to bare rock by the weight of ice. Current scholarship of the Dún Aonghasa ruins place a settlement within the inner of the four dry stone rings after 6,500 years (1,500 BC or 3,500 years ago). By way of scale, the first settlement took 30 times the duration of the U.S. Constitution ratification through 2019 and 16 times from 1,500 BC until 2019 ( 6,500 / 219 = ~30 ; 3,500 / 219 = ~16. The last state, Rhode Island, ratified the Constitution 1789).
By 700 BC, 2,700 years ago, a series of upright, closely placed stones, were erected between the second and third rings called a cheval de fries field (“Frisian horses” in English) today, this defensive structure evokes the enormous scale of the struggles around this place of defense.
This is a portion of that field, I believe, taken as Pam and I approach the inner ring entrance, walking a wide path cleared of barriers. Click the photograph for a larger image with caption.
References: search wikipedia for “Dún Aonghasa” and Google “cheval de fries definition” and “Dún Aonghasa.”