Even before Jamestown or the Plymouth Colony, the oldest permanent European settlement in what is now the United States was founded in September 1565 by a Spanish soldier named Pedro Menéndez de Avilés in St. Augustine, Florida. Menéndez picked the colony’s name because he originally spotted the site on August 28, the feast day of St. Augustine.

Menéndez’s expedition wasn’t the first group of Spanish explorers who tried to start a colony in Florida, which Juan Ponce de León had claimed for Spain back in 1513. And unlike other colonizers, he wasn’t out to find gold or set up a trading network with the Native tribes.

Instead, Menéndez’s primary mission was simple: Get rid of French Huguenot colonists who were trying to usurp the Spanish claim. The previous year, the French had established an outpost at Fort Caroline, near present-day Jacksonville. A French base in Florida posed a potential threat not just to Spanish territorial claims, but also to the Spanish treasure fleet that sailed from South America and Mexico along the Florida coast before heading across the Atlantic to Spain. Spain’s King Philip II wanted the French threat eliminated, particularly because the settlers were Protestants and to Philip, a Catholic, that made them intolerable.

Menéndez almost didn’t succeed. Philip wanted him to destroy the French colony before France could send military forces to Florida to protect it. But by the time Menéndez arrived in Florida in August 1565, he discovered that a force of French reinforcements had arrived before him, according to David Arbesú, an associate professor of Spanish at the University of South Florida and editor and translator of Pedro Menéndez de Avilés: A New Manuscript, an account of the expedition by Menéndez’s brother-in-law, Gonzalo Solís de Merás.

“He went up to the fort, by ship, where he discovered that the French had a very large fleet,” Arbesú explains. “So he retreated to a place that he had discovered the week before and had called St. Augustine, and waited for the French to attack.”

Menéndez and his men were badly outnumbered and pretty much defenseless. But then nature dealt Menéndez a lucky break.

“The French fleet appears and is prepared to crush the Spaniards, when at that exact moment, a large storm or hurricane blows the French fleet to the south and sinks them, saving the Spaniards from disaster,” Arbesú explains.

Instead of being slaughtered, “all that Pedro Menéndez had to do in the next couple of days was to walk up to Fort Caroline, which now had very few soldiers inside, and conquer it without even shedding a drop of Spaniards' blood,” says. Arbesú.

“It appears the enemy did not perceive their approach until the very moment of the attack, as it was very early in the morning and had rained in torrents,” Francisco López de Mendoza Grajales, the expedition’s chaplain, later wrote. “The greater part of the soldiers of the fort were still in bed. Some arose in their shirts, and others, quite naked, begged for quarters, but, in spite of that, more than one hundred and forty were killed.”

The chaplain praised Menéndez for “the ardent desire which he has to serve our Lord in destroying the Lutheran heretics, the enemies of our holy Catholic religion.”

When Menéndez got back to his encampment at St. Augustine, local Indians told him about seeing white men walking on the beach south of St. Augustine. “Pedro Menéndez realizes that these are the Frenchmen who had been blown away in the storm,” Arbesú explains.

Menéndez rushed to the location and found some shipwreck survivors, who had lost their weapons and food in the storm, according to an National Park Service account. Mendoza, the chaplain, asked for permission to offer the Frenchman a chance to survive if they converted to Catholicism. Sixteen of them accepted, and the other 111 were killed.

Two weeks later, French commander Jean Ribault and his surviving men showed up on the beach as well. The Spanish force offered them the chance to surrender, and the French accepted. Menéndez’s men then bound them, and stabbed Ribault to death before executing the rest of their captives by beating them to death with clubs and hacking them with axes, as Jacques le Moyne de Morgues, a French artist who heard about the killings from a sailor who had somehow escaped, later wrote. The inlet where the killings took place was named Matanzas, the Spanish word for “slaughters.”

“Had it not been for the hurricane, Pedro Menéndez's expedition would have probably failed, as all the others before him, and Florida would have been a French colony,” Arbesú says.

Instead, after the slaughter, the Spanish stayed in St. Augustine to establish a permanent colony to deter more French from settling. “Philip's support for the effort and successfully establishing a lasting settlement were in large part due to the French presence,” says Shane Mountjoy, provost of York College in Nebraska and author of St. Augustine, a 2007 history of the city.

The Spanish soon realized St. Augustine offered a valuable base for rescuers to help their trading ships when they were battered by tropical storms, as well as for warships needed to hunt pirates. As a result, the colony was heavily subsidized by the Spanish Crown. Another source of support was the Catholic church, which saw an opportunity to convert the native population, and sent missionaries to accompany the Spanish soldiers.

St. Augustine became a key center for Spanish power in Florida, which, in turn, made it a frequent target of attacks by the English and other enemies. In 1586, Sir Francis Drake raided and burned St. Augustine, but residents eventually came back and rebuilt it. In 1672, the Spanish erected Castillo de San Marcos—the oldest masonry fort in the continental United States—that still stands watch over the city.