Hi my understanding is that it was a horse market in west port meaning west market which was outside the town walls.
The museum in the town hall is a great place to start, also people such as Charles Vernon are a mine of good historical information as is our horse fair dwelling mayor, Patrick Goldstone.
The steep hill off foundry road to gloucester road was, apparently, to allow for easy cleaning of the deposits post market!
I think some of the houses are older than 1700 but open to correction
Charles has written a good book about the towns history which is for sale int he high street or in the local library
Kind regards
Andrew Carnegie