Saltier than Carthage (if it had been salted)

There is/was a social media trend, to ask your male SO how often they think about the Roman Empire. A lot of men apparently think about it more often than you'd think, and that's the whole joke I guess. Because social media.

If that's what you're saying you don't understand, then sorry for overexplaining, but I'm pretty sure that's the context for this comic and maybe it'll help future viewers.

I also don't understand why it was a trend. But I've also never understood a social media trend in my life.