I would happily follow Pratchett's advice and write 400 words a day of, well, verbiage, which could be edited next day into something respectable. But I keep getting side-tracked by unanswerable questions. Such as-- do the invading Tartars (or Mongols or troops of A/U Tamurlaine) ride *up* the grand avenue to attack the palace? in which case we're in A/U Kyoto. Or do they ride round and round the castle, looking for a way to ford the moat? in which case we're in A/U Edo.
(And if they ride round and round, do they keep passing the same group of sardonic old men sitting out front of a cafe and applauding the horsemen on each of their successive appearances? In which case we're in Carcassonne where some wag has turned all the road signs saying 'A la haute-ville' and pointing up, sideways so one kept cycling around the base of the Cité. And yes, that did happen to me.)