Civilization around the Mediterranean has been around for longer than you think, and in places the seabed is littered with evidence of that. However, authorities are very protective of their antiquities, so don't think whatever you discover diving might be there for the taking.
Witness the plight of a British tourist who thought little of the handful of old coins he found among sand and rocks while snorkeling until he was arrested on August 21st at a Turkish airport on his way home. Paramedic Toby Robyns, 52, could face up to five years in a Turkish prison if convicted of trying to take artifacts out of the country.
Ignorance of the law is no defense. At the time of writing, he's still in jail, and it may be as long as 30 days before authorities have decided whether to press charges.
In Greece, six men were arrested last month on suspicion of illegally diving for underwater antiquities off the coast of Gytheio in the Peloponnese. They were diving around the remains of a Roman shipwreck and were found in possession of archaeological artifacts, such as amphorae and lead stove tops, on shore at the site.
When it comes to the Med, dive with your eyes, take only pictures, leave only bubbles, stay out of jail.