How much citation should we expect from answerers?
Answers with significant claims (especially to historical questions) really should have a (credible) citation or two.
As Nathaniel says, deleting these would be overkill. I moderate two other sites where we have strict (and somewhat unusual) answer quality policies, backed up by deletion... and it's work. It's entirely possible, but you need to have a community that actively hunts these down and is willing to back up moderators when we invoke that deletion policy.
I wouldn't recommend that for this site, at least not yet. We wouldn't get enough benefit out of it.
Instead, let's use the usual SE method for these: downvote & comment. If we're consistent about downvoting dubious, unsourced claims, we'll naturally discourage them without placing too much of a burden on ourselves.
Obviously, we should delete crap answers like this:
lol caesar was the guy built wall around ALL OF ITALY.
Because there obviously isn't good faith there. But when it's unclear if the answer is meant seriously, we should give it the benefit of the doubt regarding deletion - but vote and comment however we (as individuals) see fit.