Hi krauton, if my parsing is correct I'm not overly fond of this clue but "some of Cicero's peers" indicates either of two possible Roman Numerals = some within trial (hearing). Look at the Chambers entry for trivial (biol).
I’ve only filled about a third of the grid but I think I’ve “got it”. Very clever, hope it all works out. Not sure about the entry for 23dn if the answer is trivial.