They had been digging for 12 years, 4 months a year, 18 hours a day. Since 1992, Georgi Kitov and his team have been searching through Bulgaria's Valley of the Kings, a 100-km, heavily forested region in the center of the country. The valley is dotted with ancient burial mounds erected by the Thracians, whose legacy as a pillar of ancient Europe lives on in texts and stories, but whose civilization remains a mystery. Kitov is slowly exploring the necropolis — and making some of the country's most incredible discoveries — in the hopes of adding to historians' limited knowledge of the Thracians, who flourished during the 5th and 4th centuries B.C. in Bulgaria and parts of modern Greece, Macedonia, Romania and Turkey before being conquered by the Romans.

Last July, he was taking a break from the valley to explore an enormous ancient temple near the central village of Starosel. But when the 62-year-old archaeologist, a short, plump man known as Bulgaria's Indiana Jones, got word that looters had been spotted in the valley — at the site of a mid-5th century B.C. tomb near Kazanlak, 170 km east of Sofia — he dropped what he was doing and rushed to the scene. Whatever was in that tomb, Kitov's crew had to get to it first. Otherwise, the tomb raiders could make off with priceless historical artifacts.

So Kitov and crew moved to Kazanlak, to a site near a spring with rumored healing powers. And they began to dig. Finally, about a month later, they struck gold — literally. Inside the tomb, they found the remains of a man who had been chopped into pieces, the bones of his legs, hands and lower jaw positioned carefully on the ground. Next to the dismembered skeleton was a life-size mask made of solid gold. Kitov was so excited, he now can't recall how he reacted. But his teammates remember him grabbing his head with both hands. "It can't be possible," he gasped. "It can't be possible."

The 2,400-year-old mask is just the first in a vast haul of treasures — including a gold ring engraved with the figure of an athlete, and a near-complete set of armor as well as bronze arrowheads, spearheads, swords and breastplates — that together amount to one of the most sensational archeological finds of recent years. The Thracian artifacts were first brought together at Sofia's National Archaeological Museum, but this week they move to a local museum in Kazanlak before heading off to Japan to appear at the World Expo in mid-June. Beautiful and intimidating, these objects bring the legends of a rich and powerful kingdom to life. "We always knew that the Thracians had great wealth from references in ancient texts," says James Sickinger, a professor at the American School of Classical Studies at Athens. "These findings show that the Thracians had wealth that rivaled that of any other great kingdom of the time."

The Thracians were known as great warriors; Spartacus, the gladiator slave who led a rebel war against the Romans, was a Thracian. And they were renowned throughout the ancient world as expert metalworkers; in The Iliad, Homer describes the Thracian King's golden armor as "a wonder to behold, such as it is in no wise fit for mortal men to bear, but for the deathless gods." With little else to go on, historians have tended to rely on ancient Greek depictions of the Thracians as a savage, tribal society that had no politics and no alphabet of its own. But after three months of digging, Kitov surfaced with over 130 pieces of magnificent jewelry, weaponry and ritual artifacts that show Thracian culture rivaled that of the Greeks. They prove that the Thracians were "not a society of barbarians," says Alexander Fol, a Bulgarian expert on Thracian history. "They had a system of values and were consciously abiding by it. This was an aristocratic society with a great hierarchy."