These 500-Year-Old Cannons May Help Unravel the Mysteries of the Coronado Expedition

In 1541, Spanish explorers established a settlement called San Geronimo III in present-day southern Arizona. Led by Francisco Vázquez de Coronado, the conquistadors were exploring what is now the American Southwest in hopes of finding riches and gold.

But not long after setting up San Geronimo III near the Santa Cruz River, the Spanish explorers encountered an Indigenous community known as the Sobaipuri O’odham. The two groups engaged in battle, with the Sobaipuri O’odham ultimately prevailing. The Spanish conquistadors fled, leaving behind some of their weapons and belongings as they made a speedy getaway.

Now, archaeologists have unearthed two of the defeated group’s 16th-century cannons. They may be the oldest firearms ever discovered in the continental United States.

Researchers discovered the first cannon in the fall of 2020 during a systematic metal detector survey of the San Geronimo III site, according to a paper published last month in the International Journal of Historical Archaeology.

They did not find any evidence of gunpowder residue on the 40-pound weapon, which is in “pristine” condition and made of bronze, the researchers write in the paper. Archaeologists think the battle may have started so quickly that the Spanish conquistadors didn’t have time to fire the 3.5-foot-long cannon.

“This cannon and the battle that occurred around it are significant in that they represent the earliest successful Native American uprising in the continental U.S. since the Spaniards did not come back for 150 years,” says study co-author Deni Seymour, an independent archaeologist who leads the excavations at San Geronimo III, to Gizmodo’s Isaac Schultz.

Archaeologists found a second cannon in March 2024, reports Live Science’s Owen Jarus. They’re still investigating the find, but they can already see that the cannon’s barrel was blown off.

“It was fired in the battle, which is when and why the barrel blew out,” Seymour tells Live Science. “[The Spanish explorers] probably put too much powder in trying to repel an onslaught of attackers who were overrunning them.”

The two cannons are also known as hook guns or hackbuts. These were lightweight weapons that were relatively easy to transport on the backs of horses, mules or humans. When used in battle, they were typically placed on large, wooden tripods and probably fired by two men.

The cannons likely fired buckshot, a type of ammunition that consisted of 86 small pellets. Researchers likened this style of ammunition to a “swarm of hornets,” they write in the paper.

“Even a single pellet, depending on where it hits, can put an aggressor out of action,” they write.

Seymour and her colleagues also found other artifacts at the site, including crossbow bolts, lead bullets, swords, daggers, chain mail and plate armor. They also unearthed European pottery, pieces of olive jars and a rowel spur.

The discovery of the weapons in Arizona shows that “the Spanish conquest, like the English and Dutch ones that came later, were precisely that: conquest and violence first; discovery second,” Sharonah Fredrick, a scholar of Hispanic studies at the College of Charleston who was not involved with the project, tells Live Science.

With her research in Arizona, Seymour hopes to learn more about Coronado’s expedition. Coronado had been serving as the governor of a province in Mexico—then called New Spain—when he first learned about the fabled Seven Cities of Cíbola. Lured by the promise of vast treasures, he launched an expedition to these mysterious destinations to the north.

Coronado’s crew of 300 Spaniards and more than 1,000 Native Americans headed north in February 1540. They never found the riches they’d been promised, but they did explore present-day Arizona, New Mexico, Texas and Kansas. In 1542, the group returned to Mexico.

Many aspects of the Coronado expedition remain a mystery to historians. But the recent excavations in Arizona may help “fill out some of the missing details,” says Matthew Schmader, an archaeologist at the University of New Mexico who is not involved with the project, to the Washington Post’s Kyle Melnick.

“That particular area, that portion of the expeditionary route, is really pretty unknown,” he adds.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.