Given Oda's love of everything mythical, it can be assumed that this is a World Egg.
from Wiki World Egg in Greek mythology
The
Orphic Egg in the ancient Greek
Orphic tradition is the cosmic egg from which hatched the primordial
hermaphroditic deity
Phanes/Protogonus (variously equated also with
Zeus,
Pan,
Metis,
Eros,
Erikepaios and
Bromius) who in turn created the other gods.
[5] The egg is often depicted with a serpent wound around it.
Many threads of earlier myths are apparent in the new tradition.
Phanes was believed to have been hatched from the
World-Egg of
Chronos (Time) and
Ananke (Necessity) or
Nyx (Night). His older wife
Nyx called him Protogenus. As she created nighttime, he created daytime. He also created the method of creation by mingling. He was made the ruler of the deities and passed the
sceptre to Nyx. This new Orphic tradition states that Nyx later gave the sceptre to her son
Uranos before it passed to
Cronus and then to Zeus, who retained it.
there is a link to Uranus. Ancient weapon Uranus? We know for a fact that Roger owned(or knew the location of) one of them.