Cicero lived 2000 years ago and is still widely considered one of the greatest orators and writers of all time. For the art of rhetoric, it really doesn't get much more authoritative than that.
I know the HN crowd is dismissive of old stuff, because fields like math and science advance fast enough that nobody calls (say) Pythagoras or Archimedes "authoritative", but the art of convincing other humans remains essentially the same.
>>themat+(OP)
I don't think it's HN; I think it's a few folks who never learned the value of history. Kind of like that kid in middle school who would say "all people in world history are dead, what do they matter?", "they didn't have iphones, so how smart could they be?", or "this wikipedia about logical fallacies disproves Plato".