Oil lamps were the primary source of illumination in the ancient world. The earliest oil lamps were probably hollowed stones containing animal fat as well as a rudimentary wick. The advent of pottery meant that oil lamps could be mass-produced by pinching the side of a wet clay dish and forming an open spout. By the Greek and Roman periods oil lamps were produced in factories and became increasingly ornate. Roman volute lamps of the 1st Century AD are particularly noted for their elaborate tondo designs.