This thread focuses on the Arsacids but there is some discussion of how the Sasanians differed and posed a greater threat, from /u/me_gusta_comer , /u/SageProductions , u/FlavivsAetivs , and myself: https://www.reddit.com/r/AskHistorians/comments/a9pqzn/the_roman_republic_was_trounced_during_its_early/?utm_source=reddit-android