there you are wrong:
greek and roman juries were selected from the populace of eligible Demos (basically Voters) men who owned land, kept their arms and paid their taxes
"Holy Roman Empire" (thats 3 lies just in the name...) appointed "juries" of religious leaders and those the religious leaders thought "pious" enough to render whatever verdict the church demanded
germanic trials (angle, saxon, dane, teutonic etc...) were all based on the "Proof" by ordeal, combat or the testimony under oath (of the ruling class only) before the king or his thanes. most "Anglo Saxon" justice was left to the victim and his family, through the ancient rites of Lex Talionis and vendetta
Cetlic trials were much more complex, with the Filidh (something like a judge, a historian, and priest all rolled into one) offering judgements in disputes or in some cases the chiefs or kings would preside while the Filidhs and Druids advised on matters of law (which was also religion)
again, this is factual, jury trials as we know them did not reappear until the 12th century during the legal reforms of Henry Plantagenet