Ancient Greek trading vessels carried more than wine
|Curvy jars called amphorae (a version from fifth century Greece shown) were often used as storage and trading vessels, as well as for decoration [Credit: Ashmolean Museum, Univ. of Oxford, The Bridgeman Art Library International]|
During the fifth through third centuries B.C., the Mediterranean and Black seas were major thoroughfares for ships loaded with thousands of curvaceous jars known as amphorae, thought from their shape to contain a drink made from fermented grape juice.
But only recently have researchers peered through the lens of 21st century genetics to identify the actual remnants of the jars’ long-disappeared cargo. Analyses of DNA fragments from the interior of nine jars from Mediterranean shipwrecks now reveal various combinations of olive, ginger, walnut and herbs in the rosemary family, along with the expected grapes.
The findings, reported in an upcoming Journal of Archaeological Science, suggest that the ancient Greeks produced and traded a wide range of foods. The economy of the time was much more sophisticated than previously thought, says Brendan Foley, an archaeologist at Woods Hole Oceanographic Institution, who coauthored the work with biologist Maria Hansson of Lund University in Sweden and colleagues at the Hellenic Ministry of Culture and Tourism.
Some of the jars selected for the study had been stored on shelves for nearly two decades, suggesting that DNA buried within the amphora walls remains viable long after the jars are brought up from underwater.
“That opens the possibility that many of the artifacts that are in museum storehouses or other collections may still contain information about their original contents,” Foley says.
With such information, scientists could reconstruct a more accurate picture of the crops being grown and the products changing hands when the world’s first complex economies were getting under way, possibly gaining clues to the agriculture, technologies, art and geopolitics that played into daily life.
Crimes and clues
A period of rapid expansion and population growth throughout the Mediterranean began around the fifth century B.C. Classical Greece was transformed from a simple peasant society to a sophisticated civilization, and Greek merchants began using currency. Instead of swapping for goods in kind, merchants were paid for their products and services with small coins of silver, gold or an alloy of the two, electrum.
To determine what was being traded for those coins, scientists look to artifacts, including amphorae still neatly packed aboard sunken merchant ships or strewn across the Mediterranean seabed.
Foley, who has recovered dozens of such containers in his deep-sea explorations, says that different civilizations from different locations and times established their own style of making amphorae. The Greek versions, with their long narrow necks and handles on either side, were assumed to be ideal cargo containers for wine and olive oil.
When Foley surveyed the scientific literature, he found 27 articles in peer-reviewed journals that directly spoke of amphora contents from Greece’s golden age. In the articles, 95 percent of the 5,860 Greek amphorae were described as wine vessels.
The finding raised a red flag, he says. “To me, it didn’t seem reasonable to assume that 95 percent of all trade goods in these jars were one commodity.”
To find out what was carried inside the jars, he turned to Hansson, who suggested searching for DNA evidence. Though some archaeologists had flirted with the idea of collecting DNA samples from the jars in the early 1990s, those researchers had little success.
Hansson says that the tools of the trade have improved dramatically since then, making today’s DNA analysis much cheaper and friendlier to use. Researchers also have access to databases of DNA information on many of the world’s plant species, making it possible to identify a specific food item or crop.
By drawing on these databases, Hansson identified short segments of DNA that show up in plants and might have been used as food, flavorings or preservatives in ancient Greece. She then synthesized small molecules, called primers, to bind to any such fragments remaining in the jar. A second round of primers targeted specific types of plants.
DNA samples were first collected by scraping the ceramic inside the jar with a steel tool. The scientists used this method to look inside two empty amphorae that Foley had recovered from a 2,400-year-old shipwreck off the coast of the Greek island Chios. The findings, reported in 2008 in the Journal of Archaeological Science, showed that one of the amphorae held an olive product, probably olive oil, flavored with oregano. The other jar probably carried wine because it appeared to contain fragments of DNA from terebinth, a plant used to preserve wine.
Looking for ways to extract genetic material without causing damage to the artifacts, Foley and Hansson continued to perfect their method. They considered pouring a buffer solution into a jar and sloshing it around to draw out the DNA fragments. After realizing that the dry jar would absorb all the buffer material, the team turned to the Massachusetts State Police crime lab.
A forensics expert there suggested a solution: taking swabs specifically designed to pick up trace samples of DNA and saturating the swabs with the buffer solution before rubbing them along the inside of the jar.
The approach worked better than the original scraping method, allowing the scientists to get more detailed information on the contents the jars carried over their lifetimes. Five of the nine jars contained grape DNA, and all of the jars contained DNA from at least one other plant species, the researchers report in their upcoming paper.
A fuller picture
But the method is not perfect. One problem is that the fragments that remain in the jars are short and not well preserved, says Hansson. Many samples contain strings of only 70 to 100 base pairs, the chemical units that make up DNA. That’s enough genetic information to tell whether a specific container carried olives or grapes, for example, but not enough to identify among herbs of the same family.
The process also may not work on items that have been exposed to sunlight or have undergone extensive cleaning, Foley says. Conservators often bathe artifacts found on land in acid, which would destroy genetic information carried within the ceramic.
Artifacts coming out of shipwrecks may also be subjected to a long rinsing process to flush out salt, believed to break up a jar and cause it to crumble to dust. To see if such rinses also wash away DNA, Foley and Hansson are preparing another round of studies. By swabbing the vessels throughout the rinsing process to extract any DNA inside, the team hopes to record if and when the genetic information degrades.
Still, the noninvasive technique provides a way to look at large numbers of archaeological artifacts in ways that were previously not possible, Foley says.
“It means that we can take the most sensitive and valuable archaeological artifacts and apply this technique to extract information from these things,” he says.
Mark Lawall, a specialist in ancient Mediterranean trade at the University of Manitoba in Winnipeg, Canada, says with only a limited number of jars analyzed so far, it has yet to be seen how much the DNA will add to what is already known about ancient trade.
“Historians were absolutely right to assume that most amphoras contained wine or oil,” he says. “Nothing in the article disproves that.”
To get a fuller picture of what was being traded, DNA data would have to be combined with other information about a ship and its contents, Lawall says. Analyzing a much larger number of jars from a single documented wreck, for example, might reveal what percentage of the cargo was wine.
Foley and his colleagues plan to take on such studies. As word of the DNA findings has spread throughout the archaeological community, other scientists are inquiring about the technique to see what their vessels were carrying. Already, nearly 100 swabs from various teams line Hansson’s freezer awaiting their chance at analysis.
“Eventually when we find the right artifacts, we can find out what the ancients were using for preservatives, cosmetics and medicines,” Foley says. “We’re going to get the first real look at all of these aspects of this critically important period when the modern world was launched.”
Author: Susan Gaidos | Source: Science News [December 05, 2011]