Why did the Saint Patrick’s Battalion change sides and fight for Mexico?

saint patricks brigade mexico

The story of how an Irish Battalion defected to the Mexican Army during the Mexican American war is a story of courage, a story of right and wrong, a story of men who answered the call of their conscience.

Known as the Saint Patricks Battalion or in Mexican as the San Patricios, the men mostly made up of Irish immigrants decided to down tools and switch sides during the brutal conflict that took place in 1846-1848.

Every year, on the September the 12th, Mexicans gather to honor the men of Los San Patricios. Flowers are placed close to a marble plaque where a list of engraved names are read. A Mexican band plays both the Irish and Mexican national anthems in honour of the sacrifices that the Irish brigade endured during the conflict.

On the 12th of September 1997 Mexican President Ernesto Zedillo paid tribute to the special sacrifice of these men where he stated in his speech:

“One hundred and fifty years ago, here in San Ángel, … members of the St. Patricks Battalion were executed for following their consciences. They were martyred for adhering to the highest ideals, and today we honor their memory. In the name of the people of Mexico, I salute today the people of Ireland and express my eternal gratitude.” The president finished by, saying: “While we honor the memory of the Irish who gave their lives for Mexico and for human dignity, we also honor our own commitment to cherish their ideals, and to always defend the values for which they occupy a place of honor in our history.”

Why they deserted


There are a number of theories that abound as to why the men switched sides.  The most common theory is that the men were subject to widespread anti catholic and anti Irish sentiment in the US Army.

And that by coming from a small impoverished land that had been continually battered, bruised, and bullied by a bigger neighbour that these Irishmen saw common cause with the Mexicans in their fight against US imperialism.

The Irish soldiers where also denied the rights to to practice their religious beliefs and where routinely flogged and beaten for any minor indiscretion, leading to simmering resentment festering against those in power. It was said that Mexicans Generals who where watching from afar noticed the ill content amongst the US Army and offered any deserters land and money for switching sides. This story may have been made up by the US authorities in an attempt to blacken the name of the San Patricos.

Another story goes that Irish catholic conscripts heard the church bells ringing in a nearby Mexican church and decided to down tools and practice their catholic faith in defiance of their commanders in the US army. Over time they built up a relationship with some of the Mexicans and found that they had much more in common with the impoverished Mexicans than they had with the greedy land hungry American army.

Another thing that must have played some part in the minds of the Irishmen was that Mexico had abolished slavery, and that the unconscionable and widespread use of slaves by the United States must have been abhorrent to an embattled and abused race like the Irish. Whatever the real story is, soldiers began to desert in droves to fight for the Mexicans.

The leader

Saint Patricks brigade mexico

The deserters where led by a man from Clifden in Co Galway, Captain John Riley. In 1846, Reilly began organising an artillery unit which was mostly comprised of Irish Catholics. This unit formed the nucleus of the San Patricios brigade.

A number of months after the creation of the unit over 200 soldiers formed part of it, which was enough to form a battalion and two companies. Some historians reckon that at the battalions peak there were over 700 men who part of the San Patricos.

Whilst the majority of the battalion was made up of Irishmen there were other volunteers of European descent. The Galway man set about forging a distinctly Irish identity to the battalion by commissioning a green flag with an image of Saint Patrick on one side and a harp and a shamrock on the other.

O Reilly when asked about what he thought of the charcater of the Mexicans stated that, “Do not be deceived by the prejudice of a nation at war with Mexico, because you will not find in all the world a people more friendly and hospitable than the Mexicans.”


saint patricks brigade mexico

The San Patricos where responsible for some the most ferocious resistance experienced by the US army during their invasion of Mexico.

At the Battle of Buena Vista, the Saint Patrick’s Battalion fought with real courage with the unit being instrumental in the capture of a large number of American Cannon. Eye witnesses described the ground held by the Patricos as, “ a strong Mexican battery….moved….by dint of their extraordinary exertions….that commanded the entire plateau.”

At one stage during the battle, The commander of the US forces General Zachary shouted in frustration at his troops, “to take that damned battery” but on that particular occasion the assault failed. Ultimately, the Mexican army were forced to retreat with the Irish contingent covering their withdrawal with ferocious tenacity.

Even though the heavily out-gunned Mexicans lost the battle the bravery of the Irishmen was acknowledged by the Mexican General Mejia who wrote in his battle report that the San Patricos where “worthy of the most consummate praise because the men fought with daring bravery.”

A number of the Irishmen where awarded the Mexican medal of honour “The War Cross” for their heroism in the heat of the battle.

But it was at the Battle of Chrubusco where the San Patricos passed into legend. In this engagement witnesses from both the US and Mexican sides stated that the unit had, “fought like demons.”

During the heat of the battle, as ammunition began to run out, the Mexican army tried to raise the flag of surrender but Officer Patrick Dalton tore down the white flag. Members of the Irish Battalion urged the men, if necessary, to fight on with bare hands.

When the Mexicans attempted to raise the white flag two more times members of the San Patricos shot and killed them. Some brutal hand to hand fighting ensued with bayonets and swords being the order of the day.

The legendary Irish brigade only surrendered when they ran out of every last piece of ammunition and weaponry and were completely surrounded by the US Army. The great American General Ulysses S Grant stated that it was “the severest battle fought in the valley of Mexico.” The Irish Battalion lost over 60% of their men in the engagement and the rest were taken prisoner.

The execution

saint patricks brigade

And so, just after down on September 10th, 1847, the villagers of San Angel a small on the outskirts of Mexico City, awoke to the sound of carts rustling into the center of the village. Inside the carts where members of the Patrick’s Battalion who where chained and bond and guarded by members of the United States army.

The carts drew to a halt beside specially constructed gallows which had been erected in the center of the village. The gallows consisted of 40 foot long beams,in which 16 nooses dangled in the Mexican air. Five Catholic Priests who were present at the time began to hear the prisoners confessions and administered the last rites.

The nooses where then placed around the necks of the prisoners and the order was given to drive the carts forward, whereby some of the prisoners fell to their deaths. Other captives where not so fortunate as they dangled in the air slowly choking to death.

A number of days after the executions at San Angel another thirty San Patricos where hanged at the village of Mixcoac. Anyone who escaped the hangman’s noose was branded and scared with a D on their face with a hot iron. The D identified them as deserters from the US army. Reilly was one of the fortunate ones to avoid the hangman’s noose.

One of the reasons for this, in spite of being instrumental in the formation of the Battalion, was because O Reilly had deserted from the US army before the war had actually began. Reillys punishment was to be branded with the D on his cheek. In all, over 50 members of the Saint Patrick Battalion were hanged, the largest mass execution in US history.

Side note

It’s also an interesting fact that the Irish have a well established history of fighting for other nations throughout Europe and the world.  In the 16th and 17th Century many Irishmen fought for the Spanish army during the continental wars, these soldiers became known as the “Wild Geese”.

Irish soldiers have also played a significant part in many South American wars for independence. During the Boer war many Irish soldiers deserted the British Army and took up arms to fight for the Boers.


The tale of the Saint Patricks battalion is a tale of people rising up against widespread discrimination and prejudice. These human beings where brutalised and discriminated against in their famine stricken homelands, and when they immigrated to another country for a better life, they were once more on the receiving end of hatred and abuse.

It seems that the members of San Patricos had enough of being treated like the refuse of the world and decided that they would rather die fighting for the Nobel cause of freedom than for the cause of imperialism, colonialism, and oppression.In the eyes of any right thinking man the San Patricos where and are heroes to the underdog standing up against impossible odds.