" So…these Pillars of Hercules. Are they dangerous?”
Annabeth stayed focused on the cliffs. “For Greeks, the pillars marked the end of the known world. The Romans said the pillars were inscribed with a Latin warning—”
“Non plus ultra,” Percy said.
Annabeth looked stunned. “Yeah. Nothing Further Beyond. How did you know?”
Percy pointed. “Because I’m looking at it. "

― Rick Riordan , The Mark of Athena (The Heroes of Olympus, #3)