Vintage engraving of Costumes of Ancient Irish Brehons. Brehon is a term for a historical arbitration, mediative and judicial role in Gaelic culture. Brehons were part of the system of Early Irish law. Brehons were judges, close in importance to the chiefs. 1815, The Costume of the Original Inhabitants of the British Islands, by MEYRICK, Samuel Rush and SMITH Charles Hamilton.