Isn't there a massive contradiction here though, on the one hand the slave can't write on the lintel and be seen in the future proving their worlds are not connected (vol 1 page 18), on the other hand there are all these artifacts that get dug up, proving that they are. Or am I misunderstanding something?
Their universes disconnect the moment they make contact, but Marcus knows Pompeii well and escapes the eruption just before it happens. So he can point Ulyses to places where things will be buried or hidden.
I also needed the relationship to go both ways, not just Marcus getting ideas from the future. That makes the plot more interesting.