Hardtack, a staple food for Civil War soldiers, dates back to Ancient Rome. It is a simple biscuit made with flour, water, and a bit of salt, and then baked repeatedly to suck out as much moisture as possible. This baking many times meant that hardtack would not spoil. In fact, some troops in the Civil War were given hardtack from the Mexican-American War 15 years before. However, it also made the biscuit extremely tough, and soldiers had to soak it in coffee or water before eating.