Omphalos

The omphalos is the stone "bullet-shaped" artifact considered at the heart of the Oracle at Delphi.

It is considered to mark the earth's "navel" (what the word means in Greek), and is said to enable prediction of the future.

The omphalos was the artifact Indiana Jones was seeking in the first adult novel (his "first" adventure aftyer graduating from the University of Chicago, in Indiana Jones and the Peril at Delphi.