On the eastern shore of the Mediterranean Sea, in far northern Israel, sits Akko, a city of layers going back thousands of years. Its “Old City,” with beautiful Ottoman architecture built on the best-preserved Crusader city in existence, is a UNESCO World Heritage Site.

Akko today gracefully blends old with new, eastern with western, religious with secular. Twenty-six religions are represented here; it is among the holiest sites in the Bahá'í and Sufi faiths. “It’s a very spiritual and cosmic place,” says Penn State archaeologist Ann Killebrew. “People who come here want to come back.”

Some of those who come back time after time are archaeologists trying to understand the previous inhabitants, who included the biblical Canaanites and Phoenicians, by unearthing and examining what they left behind. Some explore the historic old town. Others, like Killebrew, work at Tel Akko, “the hill of Akko,” a 60-80-foot-tall mound a mile east of the Old City.

Killebrew first worked here in the late 1970s, as a grad student on the first major dig at the site. “I fell in love with the place. It was my dream to come back,” she says. In 2010, she did, as co-director of a new “Total Archaeology Project” that blends a field school, sciences such as archaeometallurgy and archaeobotany, survey work, excavation, conservation, and community outreach.

The next year, members of her team were digging at a depth corresponding to about 600-400 B.C., when the resident Phoenician culture was part of the Persian, or Achaemenid, Empire. They began turning up large amounts—hundreds of pounds—of iron slag. “We’re not talking about producing for local people, we’re talking about industrial production,” says Killebrew. The more they looked, the more evidence of iron working they found, including small pit hearths, the earth beneath them vitrified from intense heat. When the team ran a magnet over the loose dirt near a hearth, it came back bristling with hammerscales, tiny flakes that break off when red-hot iron is beaten during the forging process.

Akko at that time was a major economic and administrative center for the Achaemenid Empire, which was engaged in a series of military campaigns against Egypt. It made sense that this hub of industrial activity might include ironworking, but proving that was not easy. Ancient iron work is hard to study. The few objects that have survived are usually so badly corroded there’s little left to examine. Analytical methods have also been lacking.

“I call iron the poor stepchild of archaeometallurgy, because of the structure of the metals and the kinds of analysis you can do,” says Killebrew. “Bronze you can source. Tin you can source. But until recently, iron was impossible to source.”

Identifying where a metal was mined is crucial to understanding the political connections, trade routes, and transportation systems that moved the ore from the mine to where it was turned into useful objects and then to where those objects were used. For iron, that only became possible a few years ago, when scientists at the Curt-Engelhorn Center for Archaeometry in Mannheim, Germany, developed a technique to use osmium isotopes to match an iron sample to its source. Killebrew and her colleagues sent slag from Tel Akko to Mannheim and learned that despite the presence of iron ore within a few miles of the tel, much of the iron at their dig likely came from a major source near modern Ajloun, Jordan—more than 85 miles away. Further tests showed that the ore was probably smelted near Ajloun and the resulting iron ready for smithing carried to Akko.

“They knew exactly where to get the best iron,” says Killebrew. “They were transporting it 85 miles or more. And it’s heavy. It takes a great deal of infrastructure to organize something on this scale.” That implied that the ironworks at Tel Akko were of importance to the Empire and probably under state control. But it didn’t answer the question of whether the remnants of ironworking at the site really were evidence of large-scale production. Could the small pit hearths they’d found be used to forge tools and weapons?

In the summer of 2018, Killebrew’s group did an experiment to find out. Archaeometallurgist Ümit Güder, of Canakkale Onsekiz Mart Universitesi in Turkey, spelled out their questions: What was the design of the forging hearths? How were they made? What fuel did the ancient smiths use? What was their air supply? Could these small, simple hearths generate enough heat to forge iron? What can be forged in this setting?

Here's how their experiment went:

Results of the team's experiment were unequivocal: These simple hearths could have produced iron objects on an industrial scale. Killebrew and Güder plan to recruit local blacksmiths to help with future tests of fuels and Ajloun-sourced iron.

Ann Killebrew is associate professor of classics and ancient Mediterranean studies, Jewish studies, and anthropology.

This story first appeared in the Spring 2019 issue of Research/Penn State magazine.