Behind every sharp sword that an army bears, however, is a dozen hoes, all tilling the soil for feed and ore to maintain your hordes. Although in theory an army may survive by forage, this poses logistical problems as regards to the effectiveness of your armies in the field if your enemy denies them forage by using attrition technologies researched from the Tower line. In which case, you may build supply caravans to sustain your armies in the field. Also note that siege units also benefit from the presence of a supply caravan, and will fire three times faster than they normally would without a supply caravan in place. Although they are somewhat tough, however, note that they are vulnerable to cavalry, especially Russian cavalry, and can be pillaged by an enemy for wealth.
Supply Caravans can be upgraded to Armed Supply Wagons for three factions: Mongolia, Venice, and the Papal States; however this unit can be obtained only if Republic was researched.