A team of archaeologists have uncovered the earliest European fort ever located in the interior of what is now the United States -- a discovery they say paints a painful picture of failed colonization.

Nestled into the foothills of the Appalachian Mountains, the site was settled by Spanish Captain Juan Pardo in 1567, placing it nearly 20 years before Sir Walter Raleigh's colony at Roanoke and 40 years before Jamestown, and represented the first and largest of the six garrisons Pardo founded in his quest to colonize the American South.

There's a reason, however, its influence was ultimately limited, according to the researchers.

"Fort San Juan and six others that together stretched from coastal South Carolina into eastern Tennessee were occupied for less than 18 months before the Native Americans destroyed them, killing all but one of the Spanish soldiers who manned the garrisons," University of Michigan archaeologist Robin Beck said in a press release.

Beck, along with archaeologists Christopher Rodning of Tulane University and David Moore of Warren Wilson College, is working to excavate the site near the city of Morganton some 300 miles from the Atlantic Coast.

The Berry site, as it's called, is located along a tributary of the Catawba River and was the site of the Native American town of Joara, part of the mound-building Mississippian culture that inhabited the southeastern United States between 800 AD and 1500 AD.

For years, Beck and his colleagues have been excavating several of the houses occupied by Spanish soldiers at Joara where Pardo built Fort San Juan. However, it wasn't until last month that the remains of the fort itself were found.

"We have known for more than a decade where the Spanish soldiers were living," Rodning said. "This summer we were trying to learn more about the Mississippian mound at Berry, one that was built by the people of Joara, and instead we discovered part of the fort. For all of us, it was an incredible moment."

At this point the group has identified what appears to be sections of the fort's defensive moat or ditch, a likely bastion and the graveled surface that formed the entryway to the garrison.

These discoveries, they report, were made through the use of a combination of large-scale excavations and geophysical techniques, including magnetometry, which provides X-ray-like images of what lies below the surface.

The moat itself, they discovered, measured roughly 5.5 feet deep and 15 feet across back in the day. Artifacts found in the area included iron nails and tacks, Spanish majolica pottery and an iron clothing hook used to fasten doublets and attach sword scabbards to belts.

During the brief time the Spaniards were at Joara, they were actively prospecting for gold they never found, according to the Beck. Though had they had just a bit more time, they very well may have, but instead it lay hidden until the early 1800s, at which point American settlers found so much of it that it triggered the first U.S. gold rush.

As to why the indigenous Mississipians wiped out the group, the researchers speculate that it began when the Spanish bartered with the natives for food.

"The soldiers believed that when their gifts were accepted, it meant that the native people were their subjects," Beck said. "But to the natives, it was simply an exchange, When the soldiers ran out of gifts, they expected the natives to keep on feeding them."

That, and the fact that the Spanish, according to their own documents, committed a series of "indiscretions" with the native women, were probably turned out to be a deadly combination for the group.

However, had they lasted long enough to find the gold, Beck reckons that Spain would have been much more aggressive in launching a full-scale colonial invasion of the area, making it difficult for England to ever have established a foothold.