Why I Love BBC Radio 4

What else would make it possible just to walk into a room at random and hear somebody tell you that if you'd been shopping in Ancient Rome 2000 years ago and you'd needed to go to the toilet, you'd have had 144 latrines to choose from?

I mean, how did they know? Did they ask the Doctor? There could be a whole new vein of Donna humour in this - wherever they go, the first thing he has to do is make sure there's a loo nearby.