[jamiek88]

Poor merchants, prostitutea and all kinds of people serving/scavenging from the army would follow the train in those times.

/r/askhistorians has a great thread on this, will try and find it.

[sherr]

Probably a lot of slaves as well. One has to consider how a large band of soldiers survives "in country". A lot of pillaging, ravaging and general nastiness. Slaves were a fact of life back then.