Serpent Mound in Adams County is one of the largest and most spectacular earthen sculptures in the world. The age of the serpent is a subject of much current debate with some archaeologists arguing that it was built by the Adena culture at around 300 B.C.E. and others favoring the Fort Ancient culture at around 1100 C.E. Although much about Serpent Mound still is shrouded in mystery, ancient cave paintings in Missouri may provide a key to unlocking some of its secrets.