I change my mind on this one all the time.

My book is set in ancient Rome. There are a lot of names ending in 's'

I know there are disagreements about this, so there isn't a right answer. But I still need to make a choice. I currently don't add the second 's' because this seems quite common when dealing with ancient names. (Which is why I'm posting this in the historical forum)

But I'm curious to see if anyone has any advice or has noticed trends in their historical reading.