As late as the Streets of Ankh-Morpork map, all except one of the nine city gates - eleven if you count the two water gates - have been clearly named. One, the gate diagonally opposite the Deosil Gate, remained un-named. Now we know from The Colour of Magic that Rincewind and Twoflower excape the City on the night of the Great Fire intending to go to Chirm. It makes sense that they exit the city by a gate on the Widdershins, Chirm-ward, side. Although the city gate identified with the road to Chirm is in fact the Onion Gate, if a city-wide fire is blazing, you would get out where you could. This un-named gate, therefore, is a likely candidate to have been the Widdershin Gate. On the revised city map in The Compleat Ankh-Morpork, this is identified as Trading Gate and given a name for the first time. But given its location immediately opposite the Deosil (Turnwise) gate on the other side of the city, it is not unreasonable to suggest Trading Gate has another name, maybe still used by conservative locals.