I can't see them doing too much damage on a large scale, cavalry charges would pulp their brains and shatter their bones, large headed arrows fired by the hundreds or thousands would sever a few ligaments or tendons crippling them, even quite simple traps could crush a huge number of them. Roll a huge oak tree down a hill and it would probably kill/incapacitate a village worth of zombies.
Even fairly cheap thick padded clothing or soft leathers would stop a scratch or bite, metal armour would be nigh invulnerable against individual zombies, though a horde could probably kill someone through sheer attrition regardless.
The human population at the time was pretty spread out, with a large amount living in isolated villages with infrequent contact with cities, it would require a lot of luck for a large number of zombies to congregate on any given small population, and almost all population centers had walls, gates and guard animals. Given how hard it was for a dedicated group of humans to break into most fortified places a small zombie horde would have an extremely hard time at it, gates that can withstand battering rams and catapult fire are pretty good at surviving mere bodies crashing against them. A large enough number would probably be able to break down a gate eventually, but the pressure inflicted on those nearer the gate would crush them to paste long before the gate broke.
A lot will probably get crippled by their own clumsiness while wandering around, breaking legs and spines, accumulating small cuts and gashes that would heal on a living person. Extended unceasing travel on foot would result in any shoes they had on prior to death wearing out and those with bare feet would gradually wear their own feet to mere bone stumps forcing them to crawl.
Hell, depending on how smart they are it might be possible to make them walk off a cliff to their death with just a little effort. Use a bunch of men with fast horses and loud bells to lure zombies to a clifftop with rope ladders already in place, the men abandon their horses and climb down the cliff still ringing their bells, zombies follow the noise and fall to the bottom of the cliff, shattering bones and possibly pulping brains. The men will probably die if they can't climb down the cliff and get clear before the zombies start falling past them, but even if they do the zombies will keep walking off the cliff until they get distracted by another noise.