“Don’t leave anything but footprints,” says your tour guide. “Also, don’t die.”

The latter warning isn’t an attempt to lighten the mood after a 30-minute crossing that can be brutal if the Aegean is angry that day. It’s the law.

Since 500 B.C.E., dying on the island of Delos has been illegal. Why? Don’t ask the natives. There are none. Being born on Delos is also banned. Both acts are prohibited because Pisistratus, Hippocrates’s son and ruler of ancient Athens, thought the privilege should only belong to Greek mythology’s favorite twins.

Believed to be the birthplace of Artemis and Apollo, Delos was almost as sacred as Delphi. Legend has it Leto, the twins’ Titan mother, sought refuge on Delos after being impregnated by Zeus. Artemis, goddess of the moon and hunt, was born first. Nine days later, her twin brother Apollo arrived. God of the sun and almost everything under it, Apollo was responsible for light, poetry, and art among other things. Despite their shortcomings — Apollo’s weakness was nymphs and Artemis had a pride problem — the twins were both card- carrying members of the 12 Olympians.

The Parthenon — the most visited site in Greece — receives more than one million annual visitors. Delos receives 100,000 — all day-trippers coming from other islands or cruise ships. Still, it’s not surprising. This Central Park- sized island in the center of the Cyclades is accessible only by boat. Its dozen residents are Ministry of Culture employees: guards, archaeologists and conservators tasked with preserving ancient structures and preventing the island’s other residents — stray cats who tourists love to name — from using 2,500-year- old Doric columns as scratching posts. Today, Delos is a UNESCO World Heritage site. To anyone living in the Mediterranean around 500 B.C.E. it was the center of the world.