Esperia Kingdom
So with recent spoilers about Brook and Gunko being from a wastern Kingdom called Esperia, I have some thoughts.
One of the 12 labours of Hercules was to steal the golden apples of Hesperides, the sacred fruits of the Gods, which were said to grant immortality. They were a gift from Gaia to her daughter Hera for marrying Zeus. They were kept in the Garden of Esperides which was the westernmost part of the known world to ancient Greeks (present day Morocco). Hesperides were nymphs and they were tasked with guarding the apples.
It's obvious that Oda draws inspiration from this part of Greek mythology and the golden apples of Hesperides are paralles to devil fruits in the One Piece story. So the kingdom of Esperia could be revealed to either be the place where devil fruits were created or the place where they were kept for safe keeping by the "Gods" of that era (ancestors of modern day celestial dragons maybe?).
Joyboy was said to be the first pirate. Like Hercules in the Greek myth, Joyboy might have stolen the devil fruits from the ancient kingdom of Esperia or his actions somehow caused the devil fruits to be accessible to not only the ruling class of that time period but to everyone else as well, thus leading to him being branded as a "pirate" by the "Gods".
Sorry for my english
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Another interesting bit from the Greek myth. Hesperides were not alone in guarding the apples. They were assisted by a huge serpent-like dragon, named Ladon who according to wiki " twined and twisted around the tree in the Garden of Hesperides".
Nidhogg the traitor perhaps?