On a morning in September 2020, archaeologist Deni Seymour embarked on an exciting search for artifacts along the Santa Cruz River close to Nogales, Arizona.

For several months, she had been examining the area for traces left by the Coronado Expedition led by Spanish conquistador Francisco Vázquez de Coronado, which journeyed from modern-day Mexico into what is now the United States in 1540. Her initial discovery occurred in July, and she was now diligently combing through the southern Arizona locale for additional items of interest.

Just as she began sweeping the arid landscape, her metal detector emitted a signal indicating something was buried below.

She knelt down to dig, realizing that the detector’s find was buried deeper than anticipated. As the item started to reveal itself, Seymour felt puzzled by what she was uncovering.

“I initially thought it might be a church bell or a metal container that could possibly hold a note,” she recalled.

The object displayed a greenish tint, characteristic of oxidized bronze or copper, and it was snagged in the roots of a mesquite tree. As she continued to excavate, Seymour, with her extensive background in research, felt the excitement of potentially uncovering something extraordinary.

“You have to see this!” she exclaimed to a colleague.

The item turned out to be longer than they first expected, extending beneath the soil. The excavation process lasted hours. Seymour was cautious about harming the object or displacing it from its context, requiring additional tools that a colleague brought since they were entangled in thick mesquite roots. It was a hot autumn day, with the sun glaring down upon them as they worked.

Finally, they unearthed a 3.5-foot long, cast bronze cannon.

Seymour gazed at it in wonder, feeling overwhelmed by its rarity and importance.

“At that moment, we recognized how significant this was,” she remarked.

Seymour and weapons historian William P. Mapoles documented the find in a paper published by the International Journal of Historical Archeology last year.

Their findings declared that it was the oldest gun ever discovered in the continental United States.

A unique discovery with an intriguing backstory

The cannon is classified as a wall or rampart gun, designed to be positioned on the edge of an adobe structure, a tripod in the field, or even in a tree fork in emergencies. Weighing about 40 pounds, it was heavy by current standards but light for the 16th century, making it transportable over long distances by horse or mule.

Firearms from this era are remarkably rare. Most were crafted from bronze, a costly and easily recyclable material, frequently remolded into modern designs or different items altogether. They were also prohibitively expensive, and Spanish explorers likely faced expectations to return with these weapons.

The cannon that Seymour discovered in September 2020 appeared to have never been fired. It was rudely constructed, yet not flawed. Dating techniques indicated that it had been lying beneath the rubble of a fallen stone-and-adobe structure for nearly 500 years.

So why was it abandoned?

First, Seymour needed to determine its original location.

The Coronado Expedition crossed from Mexico into present-day Arizona in 1540, advancing to what would later become New Mexico, Texas, Oklahoma, and Kansas. The precise route and the locations of various settlements remain subjects of debate, as researchers continue to gather and analyze both documentary and archaeological evidence. The expedition returned to Mexico in 1542, without the treasures they anticipated finding.

Initially, when Seymour began her exploration, she assumed it was merely a transient campsite. However, as she uncovered additional artifacts, the evidence suggested the presence of permanent structures. The site expanded in significance, revealing numerous artifacts like arrowheads, pieces of armor, ceramics, and remnants of swords and fishhooks.

While an encampment might yield between two and ten artifacts, Seymour observed that this site had “hundreds, if not thousands.” Clearly, something more significant was taking place by the Santa Cruz River.

Seymour is confident that this site was a settlement known as San Geronimo III, or Suya.

“Once we focused on Suya, I spent considerable effort attempting to disprove that notion,” Seymour explained. “Ultimately, the evidence was incontrovertible.”

She has since discovered 11 additional sites, extending from Nogales to the Gila River. Seymour believes this marks a 150-mile trail taken by the Spanish explorers, previously overlooked.

She remarked that the southeastern Arizona area holds “much more significance for the Coronado expedition during this initial contact period than we realized.”

A beleaguered settlement and a dawn raid

In 1541, conditions were dire at San Geronimo III.

The settlement was under the command of Captain Diego de Alcaraz, a leader broadly deemed unfit who inflicted brutal torture upon the local Sobaipuri O’odham people. Additionally, Seymour notes that this was where the expedition leaders relegated weaker individuals: the sick, the lazy, and the disobedient.

Initially comprising around 40 Spanish expedition members, along with family, slaves, servants, and Native allies, it was not long before a mutiny depleted their ranks by half, leaving San Geronimo III struggling with a population of around 100 people.

What transpired next, according to Seymour, explains the cannon’s abandonment.

She believes that the O’odham waged a surprise dawn attack that left the Spanish explorers desperately fighting for survival.

Historical accounts suggest that the O’odham were quick and effective, leading to many deaths among the Spanish in their sleep. It is also suggested that O’odham tribes from surrounding areas possibly unified in their assault on the settlement.

Seymour theorizes that the structure where the cannon was found could have been one of the first to be targeted.

Using the cannon would have been challenging, Seymour explains. Consider the process: adding gunpowder and shot, securing it with paper or grass, lighting a match from embers, igniting the cannon, and waiting for it to fire.

“Such a process takes time,” she noted. “If you are being overwhelmed by hundreds of O’odham, you likely won’t have time to load a cannon like that.”

She suspects that the individual handling the gun was either killed or fled without retrieving the 40-pound cannon.

“Most people were killed, and the survivors likely fled with hardly anything to their names,” she stated. “They probably only had the clothes on their backs.”

Thus, the cannon was left behind, buried and hidden for nearly 500 years.

A second cannon, but in poor condition

Last year, Seymour excavated a second cannon from the same site. This one was located in a region where most of the fighting seemed to have occurred, accompanied by numerous projectiles and other artifacts.

This cannon was fired during the attack, and its side had blown out, likely due to poor construction.

“What we suspect is that they may have made a desperate attempt, overloading it with gunpowder and shot to stave off being overrun,” she explained.

Seymour indicated that both cannons likely originated from the same foundry in Mexico or the Caribbean, suggested by their relatively poor craftsmanship and absence of maker’s marks. If true, this would make the cannons the oldest surviving firearms crafted in the Americas.

While the evidence supports this theory, confirming it would necessitate cutting into the cannons for analysis, which Seymour opposes, expressing her desire not to damage such invaluable artifacts.

Indigenous O’odham play a pivotal role in the narrative

As Seymour recounts the story of the battle, she emphasizes her belief that the mutiny—the key weakening of San Geronimo III—was a response to Alcaraz’s brutal conduct toward the O’odham.

She finds it crucial to highlight “voices of reason amid atrocious actions.” She remarked, “If we remember this, we might also be more inclined to resist injustice ourselves.”

Her professional focus centers on the period of initial contact between Native Americans and Europeans—a subject she has explored for decades.

Seymour continues her excavation work in southeastern Arizona, eager for further insights about the Coronado Expedition and its interactions with Native Americans.

Previously, it was believed that the expedition had either overlooked the area or passed through quickly, leaving no trace of the Spanish explorers behind. However, Seymour’s discoveries in southern Arizona have fundamentally altered her understanding of what transpired.

“It has become evident that the O’odham are central to this narrative,” she noted. “They provided significant resistance to the Spaniards.”

The discovery of the oldest gun in the continental U.S. has generated considerable media attention for Seymour since the publication of her paper.

Although the title of the oldest cannon is significant, the real value lies in the tangible connection it offers to the past.

To Seymour, it represents not just the Europeans who used it but also the Native Americans who confronted it and the complex interactions that occurred between these groups five centuries ago.

“When I show people this cannon,” she said, “they feel a connection to history.”