There are basically no non-sentient lifeforms of a size that could, and would be willing to, pull wagons from city to city.
The only lifeforms that physically could, are sapient.
Medieval, so no trains.
The only realistic alternative I see is using ships and boats.
Convenient and non-taxing transport for people is also a factor, and seems to fall into the same alternatives.
I imagine this would make a Venice-like canal city a more likely; Intra-city transport would effectively require the canals, no?
(The ecological effects of not having the multitude of lifeforms performing the various roles (Bees, for instance), are hand waved, so not part of the question)
I am somewhat uncertain if this is even an appropriate question.