Omphalos

The omphalos (or omphalus) is also called the umbilicus or navel.

'Omphalos' is the Greek word for the navel.

The decorative boss protruding from the center of a Greek warrior's shield was also called the omphalos, as was the knob at the center of a yoke.

The omphalos was the 'center of anything.' The omphalos in the temple of Apollo at Delphi was a rounded conical stone; it was sacred and marked what the ancient Greeks believed to be the central point of the earth.

They must have similarly believed that the center of a person was their navel -- the omphalos