Archaeologists use X-rays to distinguish iron from different periods of America’s colonial past
On a dark night in late May 1543, a group of men snuck through the Native American town of Guachoya and stopped at the gated wall, where a body had recently been buried. Working quietly, they disinterred the body and carried it to a nearby river, where they wrapped it in shawls filled with sand and dropped it in the water. Thus ended the brief and brutal history of Hernando de Soto, a Spanish soldier who helped conquer Nicaragua, overthrow the Inca empire in Peru and famously led an extensive expedition and military campaign from present-day Florida up through South Carolina and west to Arkansas.
His men had decided to bury his body at first, but given that he’d convinced the Indigenous inhabitants that he was a god before he died of an unknown illness — a decidedly ungodlike thing to do — they later committed his body to a tributary of the Mississippi River, hoping no one would find him.
De Soto’s expedition represented the longest sustained 16th-century incursion of Europeans into North America, but it was preceded and followed by several others, 15 in all. That’s a problem for archaeologists. The Spanish left behind detailed records of their exploits in the Americas, but because they only had a vague sense of where they were at any given time, the exact routes they took remains unclear.
Archaeologists have sidestepped this issue by looking for things the Spanish left behind, especially iron, which they brought with them in great quantities. But the various expeditions, which often overlapped, makes things complicated.
“A wrought-iron nail from the 1500s looks like a wrought iron nail from the 1600s,” said Charles Cobb, the Lockwood chair in historical archaeology at the Florida Museum of Natural History.
Nails account for more than half of all metal artifacts found in North America. This, of itself, is no small problem, said Lindsay Bloch, a courtesy faculty member at the Florida Museum and principal investigator at Tempered Archaeological Services. “Archaeologists find lots and lots of rusty nails and other rusty iron objects. We often can’t even tell what they are, so they get weighed, counted and put back in their bag. And usually, no one ever looks at them again,” she said.
The Spanish had more than just nails. They used iron to make axe blades, horseshoes, breastplates, helmets, spokes, spears, knives, guns and more. They even brought along blacksmiths and farriers on their expeditions to repair and repurpose things on the go. But these objects, like nails, are typically indistinguishable through time. From the moment Christopher Columbus laid anchor in the Bahamas through the conquest of Florida, there were too few changes in the style of metalworking for there to be readily observable diagnostic differences between iron objects made by the Spanish.
That may be about to change. Both Cobb and Bloch are coauthors of a new study in which they demonstrate that microscopic differences in iron from this time period can be spotted using X-ray fluorescence spectrometry. They made this discovery by analyzing objects of unknown affinity, which they now think may have come from the de Soto expedition.