Archaeologists excavating a sprawling prehistoric fortress in southern Greece have discovered a secret underground passage thought to have supplied the site with water in times of danger.

Dating to the mid-13th century B.C., the stone passage passed under the massive walls of the Mycenaean citadel of Midea and probably led to a nearby water source, authorities said Friday.

The passage would allow the people of Midea, about 93 miles south of Athens, safe access to drinkable water even in times of enemy attack.