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During the dawn of the Cycladic Bronze Age, a gleaming white monument rose up out of the Aegean Sea. A manmade network of terraces and buildings constructed out of more than 1,000 tons of imported white stone, the massive monument took up practically every inch of the Dhaskalio promontory that was once connected to the Greek island of Keros.

Thousands of years later, Keros is an uninhabited and protected archaeological site. Time has weathered the monument and rising sea levels threatens Dhaskalio. But thanks to a recent excavation, a team of international researchers are digging into the island's thriving but mysterious past.

"It must have been absolutely striking to approach that from the sea," says excavation co-director Michael Boyd. "The island itself is visible from quite some distance."

A Sophisticated Society

Archaeologists have known that ritual practices took place on Keros 4,500 years ago, and past excavations have unearthed a sanctuary and thousands of marble sculptures. Experts believe the objects were made elsewhere, intentionally broken, and brought to the island for burial.

As the oldest excavated site on the island, the sanctuary likely drew people to Keros from nearby lands, Boyd says. With them, they brought food, metal, and the volcanic glass obsidian, among other raw materials. Keros grew to be a sophisticated metropolis over time, complete with experienced metalworkers and engineers. It's the largest known Cycladic monument to date.

"Everything else seems to follow just a little bit after [the sanctuary]," says Boyd, a fellow in the archaeology department at the University of Cambridge. His co-director, Colin Renfrew, is a National Geographic explorer.

Armed with iPads, a digital excavation system, and a National Geographic Society grant, the team located a complex system of plumbing under the structure's stairs and within its walls. This shows the islanders carefully planned and built their architecture; their sophisticated drainage system dates back 1,000 years before other known systems. Future testing will determine if the plumbing was meant for freshwater or sewage. (Read: "Mysterious Disk Found in Ancient Greek Shipwreck")

Metal melting and casting was common practice in the islanders' society, and the archaeology team found two workshops during their excavation. In one, filled with debris and other objects, they uncovered a lead axe, copper dagger molds, and dozens of copper-coated ceramic fragments, including a piece that would have been part of a pair of bellows. In the second workshop is an intact clay oven, which will be excavated this year.

The discovery of metalworking and engineering shows this society was particularly complex. Researchers have known metalworking was popular around the third millennia BC, but this society's innovative technology was most likely unique to its people. (Read: "How Archaeologists Discovered 23 Shipwrecks in 22 Days")

"We probably are dealing with a kind of expertise that was not widely shared," Boyd says.

Island Imports

Boyd says there are no obvious resources on Keros, except for maybe some undesirable marble. There was a spring located on the island, but farming would be difficult and the large-scale agriculture that would have been needed to support the highly populated island was practically impossible.

All the resources that have been found on the island would have needed to be imported. The tons of white stone that made up the monument would have likely been brought in from Naxos, an island located more than six miles away. Although Dhaskalio was naturally pyramid-shaped, the artificial terraces the society constructed would have given it a more monumental appearance. (Watch: "Ancient Ruins Discovered Under Lake in Turkey")

Metalworking materials would have been imported as well, since there were no metal ore sources on Keros. Food also needed to be brought in, says Evi Margaritis of the Cyprus Institute. In soil samples, the archaeologists found traces of dried seeds, grapes, olives, figs, almonds, and cereals like wheat and barley. These traces could hint at how agricultural strategies developed over time.

The soil is still being investigated, and the archaeologists are hoping to find burnt wood or seeds, plant remnants, and the bones of fish and animals. Further chemical analysis on pottery and grinding stones could also provide clues about food production and consumption on the island.

A Lasting Legacy

With its dense population and plentiful imported resources, the island would have been an important, central location for Cycladic islanders.

"It just gives this impression of being a very cosmopolitan and international place," Boyd says.

This year will be the final season for this team's excavation of the island. Starting in early September, they'll search trenches on the island to see how they connected groups of buildings. Boyd is hopeful they'll be able to reach the floors at the bottoms of those trenches, which could give clues about the different types of activities that took place there. The team might also be able to find out what earlier phases the foundations went through.

But, Boyd says, one question remains unanswered.