One of the largest problems with maintaining a large standing army is the food supply. The Roman army was no exception. Each soldier ate about 1/3 of a ton of grain a year. It is estimated that just the soldiers in Britain ate over 33.5 tons of grain a day. A soldier always marched with at least a good supply of bacon, hard tack biscuits, and sour wine. An army was often accompanied by a herd of cattle, a mobile food source.
While the soldiers were on long campaigns, such as Caesar's conquest of Gaul, the supplies would run low, and the army would take from anyone it passed.
When on station, the soldiers ate considerably better. They always maintained a herd of cattle, sometimes herding other animals such as sheep and goats, grew grain and other crops, including vegetables, and foraged for variety. Naturally, the diet varied somewhat, depending on the terrain, as some crops could not grow in certain areas, and the local fauna varied. For example, a unit in Corbridge is known to have eaten hares, deer, foxes, badgers, beavers, voles, wild oxen, and moles, while one in Benwell ate fresh-water mussels, and a unit in the Valkenburg ate a variety of poultry, such as chicken, duck, petrels, cormorants, herons, spoonbills, mallards, teals, geese, cranes, and crows.
Another source of food in the army was contributions from friends and family members. Many letters have been recovered on this subject and the matter of payment surrounding it. In fact, this is where much of the information on the soldier's diet comes from.
Perhaps the most significant fact about the Roman soldier's diet is that there are no recorded complaints about it.