Between everything else, I’ve spent the last two weeks putting the final touches to my Pompeii book which is coming out in September in the UK and in November in the States (dont be confused by the different titles -- it's the same book). I haven’t done this as often as some – but my experience is that however much time you leave for checking the proofs etc, it never feels quite enough. And, no matter how many times you’ve looked things up, there always seems to be more to be done.
Mostly, it is the ‘have I left the iron on?’ phenomenon. Although you are at some level quite confident that those references to Pliny are actually right, once you’ve raised that tiny doubt in your mind, all you can do is check them again. And, of course, just like with the iron (which I did once find burning away, after I’d driven back from work) , every now and then, there really is some howler waiting to be discovered.
My own particular Achilles heel is the town of Cnidus.