A pie is a baked dish which is usually made of a pastry dough casing that covers or completely contains a filling of various sweet or savoury ingredients.
The need for nutritious, easy-to-store, easy-to-carry, and long-lasting foods on long journeys, in particular at sea, was initially solved by taking live food along with a butcher or cook. However, this took up additional space on what were either horse-powered treks or small ships, reducing the time of travel before additional food was required. This resulted in early armies adopting the style of hunter-foraging.