William Hayes Ward (1910) discovered that symbols similar to the classical caduceus sometimes appeared on Mesopotamian cylinder seals. He suggested the symbol originated some time between 3000 and 4000 BC, and that it might have been the source of the Greek caduceus. A.L. Frothingham incorporated Dr. Ward's research into his own work, published in 1916, in which he suggested that the prototype of Hermes was an "Oriental deity of Babylonian extraction" represented in his earliest form as a snake god. From this perspective, the caduceus was originally representative of Hermes himself, in his early form as the Underworld god Ningishzida, "messenger" of the "Earth Mother".