Primum Mobile

Primum mobile is an idea from ancient Greek and Roman times. It was an explanation of why things move in the world. People then thought that the world was made up of four elements - air, earth, fire and water. They believed that these elements were held together and kept in motion by a mysterious force called the primum mobile, which was like a "first mover" that kept everything in motion. It was like a big wheel that never stopped turning. So, whenever something seemed to move in the world, people thought it must be because of this mysterious primum mobile.