“A pair of ashen Aos Si faces peeked from under the flap, their lolling mouths bobbing with every motion. The severed heads were tied to the rider's saddle by the once ornate braids of their long hair. These trophies were not old relics of the days when some Aos Si openly roamed the land, claiming bounties for their lord. Their necks had gleaming red edges where they'd been severed. Recent kills.” - Riona, Shelter and Sacrifice
Researching for Shelter and Sacrifice, Exiles of Eire book four, needed me to look deeper into what the Aos Si were like before the walls of Tir Na Nog closed. I researched into the ancient Celts, since their culture is what has been my biggest inspiration for building the Aos Si.
Sources for what Celtic society was like, especially on continental Europe, are mostly from bias, second hand accounts of Romans who encountered them at the time. Modern research has shown the Celtic civilization to be deeper and richer than these older accounts painted it to be. However, some bloody practices have other archeological finds to support their existence.
One of these is headhunting. Celts believed that the soul, the essence of a person, was in their head rather than in their chest or stomach. Enemies' and family's heads were saved as trophies and mementos. There's even evidence of a possible "cult of the severed head" existing, being depicted through carved symbols and whatnot. Some Celts became hired mercenaries, and Romans wrote about them being very effective when hired, and the practice of tying enemies' heads on their saddles being a useful way to count how many kills they had made.