I just finished Simon Scarrow's 'The Legion' novel, and there was one part that confused me. Usually I find that his facts are sound, but early in this novel, when a century of Roman marines storm a ship, it says they were lead by a decurion. The quote is a bit awkward, but it will post it. Note that Diodorus is the marine leader, and Cato is a prefect:
"Diodorus was squatting beside one of the bodies and Cato joined him. 'There's little sign of corruption'. The Decurion sniffed and..." (it is on page 23 if you have a copy of the book)
It is the only reference to Diodorus's rank in the book, and while I took for granted that he was a marine centurion, this quote shows that he was a decurion. I always believed the decurions to be in charge of cavalry, not infantry - and certainly not Roman marines. So I am wondering if decurions did actually serve in the Roman navy (it seems unlikely to me), or if Mr. Scarrow got a really simple fact wrong (that also seems pretty unlikely.
Thanks for the help.