eli5: How did old militaries (such as ancient Rome) manage to keep fed and hydrated thousands soldiers in long military campaigns over long distance and time?

Question

eli5: How did old militaries (such as ancient Rome) manage to keep fed and hydrated thousands soldiers in long military campaigns over long distance and time?

In: 8

Answer 1

Combination of supply lines with livestock etc. and confiscating local goods. It beat the previous methods, which usually involved living off the land.