The San Patricios deserted the U.S. Army to fight for Mexico. To this day, their legacy lives on

Mexico and Ireland flags
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A small but mighty troop of Irish-born soldiers would defend their faith and defy the United States, a country where they sought freedom. El batallón de San Patricio, defectors from the U.S. Army, stood in solidarity with Mexico during the Mexican-American War of 1846-48.

Nearly 180 years later, historians, scholars and writers still find themselves engrossed by the story of the San Patricios.

Their proud Irish identity and religious conviction became a symbol of unity and camaraderie that was carried throughout the battles. Historically, the San Patricios, led by Irish native John Riley, have been valorized as unsung heroes and criticized as turncoats.

History: The two countries honor St. Patrick’s Battalion, a group of immigrant Irishmen who deserted the U.S. Army and joined with the opposing forces in the Mexican-American War of 1846.

Sept. 16, 1997

“In the United States, they’re largely reduced to certain Leftists or activist circles. But that’s true for the broader American understanding of the Mexican-American War,” said Alexander Aviña, an associate professor of history at Arizona State University.


A nativist movement built on anti-Catholic sentiment and Anglo-Saxon supremacy ran rampant in America during the 1840s. For the Irish Catholics who escaped poverty, prejudice and colonization under British rule, they arrived in the U.S. only to be met by similar derision.

“How can a country that was born out of an anti-colonial, anti-imperial revolution turn around and become an empire and invade a neighboring country? That’s what they did in 1846,” said Aviña.

Between 1844 and 1849, an influx of Irish immigrants left their ancestral lands to escape religious tyranny and famine — the so-called “Great Hunger,” caused by a destructive mold that wiped out much of the country’s potato crop, which resulted in more than a million deaths and the displacement of at least a million more. With this flow of mass migration, anti-papist aggression reawakened racist rhetoric that circulated in the press.

“I think there were 3,000 books published during this period showing how Catholicism was an abomination and if you were a Catholic, your allegiance was to the Pope rather than to the president or Congress,” said Michael F. Hogan, author of “The Irish Soldiers of Mexico.” The 1997 book inspired an MGM film and two award-winning documentaries.

Along with nativist beliefs, the concept of Manifest Destiny had also taken hold. The ideology was rooted in westward expansion, which began with Texas. The U.S. was eager to acquire more of Mexico’s land, at one point offering $5 million for the province of New Mexico and $25 million for California. “[America] wanted to have the sea to the shining sea,” Hogan said.

Hogan, emeritus chair of humanities at the American School Foundation of Guadalajara, was intent on providing the “other side” of the San Patricios, one not commonly examined in U.S. history.


“I wanted the book to discuss how America evolved. And part of it was the ‘city on the hill’ that was not open to other faiths and races,” Hogan said. “Americans were not defined by who they were, but by who they weren’t.”

In the spring of 1846, U.S. soldiers and the Texas Rangers set fire to El Fronton, a port town on the Texas gulf along the border. This incident left an impression on many Irish immigrant soldiers, who were reminded of stories they heard from relatives who survived religious persecution.

Among the service members was Riley. At 28, he emigrated from Galway, Ireland, to Michigan and enlisted in the U.S. Army at Fort Mackinac, where he would instruct West Point cadets.

Many immigrants fled their country and joined the Army — it was a chance to earn a living. But like Riley, many “regulars” encountered harassment and beatings, and were called racial epithets by their officers.

Across the Rio Grande in Matamoros, church bells would ring and the spired cathedrals would remind the Irish soldiers of the old world. The clergy spoke the universal language of Latin as they blessed Mexican infantrymen.

War: Irish immigrants who deserted Army and took up arms against the U.S. in Mexican-American conflict are recalled in books and film and will be remembered in St. Patrick’s Day parade.

March 16, 1997

Sensing an opportunity, Mexico began a counter-propaganda strategy by sending leaflets to U.S. soldiers, namely Irish and Germans, to plead for their cause.


Pedro de Ampudia, a Cuban-born general in the Mexican army, wrote letters to U.S. soldiers to ignite their “indignation” about the cruelty “under the flag of stars.” In addition to tapping into their political consciousness, he provided incentives: land ownership, pay increase, mobility in rank and religious freedom.

On April 12, 1846, Riley requested a pass to attend a Catholic service. Instead, in the evening, he took the chance and crossed the river.

When Ampudia met Riley, the general was impressed with the Irishman’s intelligence and commissioned him as a lieutenant. Riley chucked his American uniform for the rich blue coat of Mexico. With minimal convincing, Ampudia agreed to let Riley form an artillery unit and entice potential deserters. And so, at Matamoros, he formed a company of 48 Irishmen.

The San Patricios fought numerous battles, traversing rough terrain and enduring horrid conditions. In each armed conflict, they were reminded of their motherland and were further radicalized, witnessing the dehumanization of Mexican civilians.

Leaders of the Mexican army noticed soldiers who “viewed the kind of war crimes that some of the American forces, particularly the volunteer regiments, were committing in Mexico,” Aviña said. “The Mexican political-military leadership recognized that and did their best to amplify anti-Catholic riots that were going on at the same time in the United States.”

The San Patricios would proudly fight beneath their makeshift flag — emerald silk that bore the Mexican coat of arms with a golden harp encircled by shamrocks and the motto “Erin Go Bragh.” On the other side stood a figure of St. Patrick.


But they would meet their tragic fate as they moved to protect areas near Mexico City as the U.S. Army’s invasion reached the capital. Newly promoted to brevet major, Riley led 143 Irishmen as they marched to Churubusco. They fortified their position in a towering stonewall monastery, but after a three-and-a-half-hour battle, the San Patricios ran out of ammunition.

Out of the 85 San Patricios captured, 71 soldiers were split into groups and executed at the gallows. The verdicts came swiftly with no trial.

Col. William Selby Harney, who had previously evaded prosecution over assault and murder allegations, oversaw the final execution. As daylight broke on Sept. 13, 1847, the American forces charged Chapultepec Castle, the citadel securing Mexico City. Harney waited until the U.S. signaled its “victory” and ordered the remaining San Patricios to be hanged.

“Not only were these cruel and unusual punishments contrary to our Constitution, but they were also contrary to the Articles of War and our court martial rules and regulations,” Hogan said.

Riley technically deserted before war between the neighboring countries broke out, so he escaped the mass hanging. Those who survived were subjected to lashings, were branded with a letter “D” on their cheeks by a cattle iron and were imprisoned. Riley was branded twice; the first one was accidentally upside down.

The invasion against Mexico saw a staggering number of deserters. Of an estimated 40,000 regulars, more than 5,331would defect — including nearly 1,000 Irishmen. However, many Irish volunteers remained, including second- and third-generation Irish, who had assimilated into American life.


“Those who had deserted would receive full pardons,” Hogan said. “It was only the San Patricios who were treated that way.”

The last recorded information on Riley was that he left for Veracruz with a $1,224 pension. Some speculate he returned to a son in the verdant pastures of Ireland.

The Treaty of Guadalupe Hidalgo was signed on Feb. 2, 1848. Mexico was paid roughly $18 million by the U.S., and in turn ceded two-fifths of its territory, including present-day California, Nevada, Utah, New Mexico, parts of Oklahoma, Kansas and Wyoming and most of Arizona and Colorado.

“In a way, the war never ended. When we think about the cyclical border panics that we see about the U.S.-Mexico border, all that is a consequence of how this war was resolved, or rather how it was not resolved between Mexico and the United States,” Aviña pointed out.

There are lessons that can be gleaned from the San Patricios.

In 2022, Simon & Schuster published “A Ballad of Love and Glory,” a historical novel written by Reyna Grande based on the battalion. Grande says she felt like the story of the San Patricios should have been taught to her in school.

“It was a very empowering journey because once I started to learn the history, it helped me to reframe the way I saw myself as a Mexican living in California and especially as a Spanish-speaking immigrant and also how my story fits into this larger, social, historical, political context of immigration,” said Grande, who entered the U.S. at the age of 9.


The U.S.-Mexican border crisis, including the effects of family separation, was a way to connect with the characters in the book, she said.

“I gave John Riley my immigrant trauma because he was dealing with a lot of prejudice that I feel as a Mexican immigrant and my community has experienced,” Grande shared.

In observation of the San Patricios, Grande’s book was a way of keeping them in conversation while honoring their memory and ensuring they were not forgotten.

Every September, a ceremony at the Plaza San Jacinto in Mexico City commemorates the anniversary of their wrongful death. A bust of John Riley sits near a plaque memorializing those martyred. Other celebrations are held at battle sites, like the Museo de las Intervenciones in Coyoacán or on St. Patrick’s Day, including one at the Irish Embassy in Mexico City and another at the Ex-Convento de Churubusco. In Ireland, the San Patricios banner proudly waves during parades.

For Hogan, the message of the San Patricios and the invasion comes down to tolerance. “Once we start teaching history solely from a nationalistic level, we lose a sense of tolerance. ‘Why should we be tolerant? What does it profit us to be multicultural?’ We need to be taught those things. As long as that fear exists, there will be violence and there will be wars.”

Sarah Quiñones Wolfson is a Los Angeles-based journalist with experience crafting stories focusing on the intersection of arts, culture and social justice. She has written for outlets like the Los Angeles Times, Hyperallergic and KCET.