A millstone is a large, round stone used in the process of grinding grains into flour. Traditionally, two millstones are used together: a stationary bottom stone and a rotating top stone. The grains are placed between the stones, and as the top stone turns, it crushes the grains into a fine powder. Millstones have been used for centuries in various cultures and are often made from durable materials like granite. They are an essential part of the milling process, which is crucial for producing staple foods like bread. Today, while modern machinery has largely replaced them, millstones are still found in some traditional mills and are valued for their historical significance.