Millstones are large, round stones used in the process of grinding grains into flour. They typically consist of two parts: a stationary base stone and a rotating top stone. The grains are placed between these stones, and as the top stone turns, it crushes the grains into a fine powder. Historically, millstones were powered by water or wind, making them essential for early mills. They are often made from durable materials like granite or limestone, which provide the necessary hardness for effective grinding. Today, while modern machinery has largely replaced them, millstones remain a symbol of traditional grain processing.