MORGANTINA, Sicily—Three thousand years ago, this broad ridge 50 miles west of Mount Etna was the perch of a magnificent city. Its monumental architecture and refined art, its irrigation systems and agricultural wealth, made it a leading Mediterranean power half a millennium before the rise of Imperial Rome.

Today, most of its wonders lie under acres of wild fennel and oleander. In several hours amid the ruins, this reporter encountered only five tourists, two unpaid volunteers, and not a single guard or maintenance worker. Ancient Morgantina is among archaeology’s most neglected secrets.

But it is no secret to tomb robbers, who have made it one of the most looted historic sites on the planet, or to the extraordinary army that battles