“The Irish Diaspora: Tales of Emigration, Exile and Imperialism” by Turtle Bunbury; Thames & Hudson (304 pages, $34.95)

Ireland’s greatest export always was its people.

Some fled famine, violence or poverty. Others sought love, adventure or fortune. And Turtle Bunbury’s “The Irish Diaspora: Tales of Emigration, Exile and Imperialism” pays them tribute.

The word diaspora comes from Greek for “I scatter,” and ancient Ireland was settled by wanderers, Stone Age settlers from some forgotten land. Yet no sooner was there an Irish people than they were headed somewhere else.

Some went as missionaries. By 590, St. Columbanus was spreading the Gospel, starting in France and heading west. His proselytizing was aggressive, too. In Austria, he surprised a “barbarian horde” about to offer up a barrel of beer to their god, Wodan. An outraged Columbanus breathed on it, and it miraculously burst open.

“Establishing facts is notoriously difficult when it comes to validating the lives of pioneering holy men like St. Columbanus,” Bunbury writes. “Much of our apparent understanding of such people is based upon semi-fictional, semi-romantic hagiographies.”

The participants’ reaction to all that good beer going to waste was not recorded.

Other Irish holy men traveled as far north as Iceland, and some might have gone further. Brendan the Navigator was famous for his 6th century seafaring. Bards spread stories of the saint’s fanciful encounters with sea monsters and with a marooned Judas Iscariot. Later, some claimed the wandering monk discovered America, too.

In 1976, adventurers built a replica of Brendan’s leather-skinned boat and set out from Ireland to prove the old sailor could have done it. They made it all the way to Newfoundland.

Other Irish travelers were far from saints. The son of a failed brewer, Richard Brew, left County Clare in 1745 to make his fortune. He found it in Ghana, becoming a notorious slave trader. Men and women were packed together on ships like “herrings in a barrel,” one abolitionist wrote. Brew’s contemporaries described him as “unscrupulous and hard-headed.”

Being crooked and stubborn was no disadvantage in the slave trade. Brew soon bragged of his “genteel fortune” and built an incongruous Georgian mansion on the African coast, complete with paneled library and crystal chandelier. Ultimately, though, he had more creditors than sense. Brew was bankrupt when he died at 50 in 1776.

Similarly notorious was Pat Watkins, the “Crusoe of the Galapagos.”

It was Capt. David Porter of the U.S. frigate Essex who first wrote of Watkins. In 1812, Porter landed on Charles Island, a remote spot in the Pacific chain, expecting it to be uninhabited. Instead, he found a solitary redhead. “Ragged clothes, scarcely sufficient to cover his nakedness,” Porter noted. “So wild and savage in his manner and appearance that he struck everyone with horror.”

The Irishman said he had been there for five years, although not whether he’d been shipwrecked or deliberately marooned. His ill temper and crude behavior suggested the latter. The man, a disgusted Porter wrote, represented “the lowest state of which human nature is capable.”

Eventually, though, even Watkins grew tired of solitude. When other ships landed, he coaxed their sailors to join him. Later, five of them helped him steal a boat, and they all sailed for Ecuador.

Watkins, however, arrived alone, suspiciously claiming everyone else had died en route. He made his way to Peru and was pursuing “a tawny damsel” when the police caught up with him. Charged with “improper intentions,” he was dragged to jail and never heard from again.

Other Irish wanderers were more idealistic, taking up the cause of freedom. Born in County Wexford in 1611, William Lamport went to London to study and to publish satires about the monarchy. Fleeing England one step ahead of the authorities, he was captured by pirates. Proving himself adaptable, he joined their crew.

Lamport re-emerged in Spain as Don Guillén Lombardo, a dashing swordsman known for “a beautiful face and figure.” He spied and soldiered for the Spanish crown while trying to drum up support for an Irish rebellion. Guillén left Spain in 1640; the seduction of a noblewoman may have prompted his exit. Eventually, he wound up in Mexico.

Never one to think small, Guillén now dreamed of beginning his nation, free of slavery and superstition. He plotted to seize Mexico City and proclaim himself this new country’s ruler. He failed, of course, and was imprisoned. Naturally, his criticism of the Inquisition drew attention. Charged with heresy, he was burned at the stake in 1659

He, though, lives on — at least fictionally. Some 260 years later, he inspired American writer Johnston McCulley, who gave him a new name: Zorro.

The Irish fought for America, too. A successful Manhattan tailor, Hercules Mulligan, chatted up British officers, then turned around and passed the info to colonial patriots, including his friend Alexander Hamilton. Twice, Mulligan foiled plots to assassinate George Washington, who proclaimed him “a true son of liberty.”

A century later, the Irish immigrant “Little Al” Cashier fought for the Union, serving with the 95th Illinois Voluntary Infantry. What none of his colleagues knew was the beardless youth was born Mary Hodgers. Later, though, a few remarked on Cashier’s eccentricities, like doing the other soldiers’ washing and mending. Cashier “always insisted on bunking by herself,” one added.

Cashier left the Army with a pension, moved to Illinois, continued to live as a man, and worked as a gardener and chauffeur. His secret was discovered in 1911 when Cashier was struck by a car and examined by doctors. Sadly, later, suffering from dementia, he was committed to a state hospital. Authorities put him in the women’s ward and made him wear skirts. Cashier declined rapidly and died in 1915.

Most Irish emigrants lived far quieter lives. Not all left home willingly, either. Some were exiled by Oliver Cromwell in the 1650s, sent to Jamaica as indentured servants. Later, others, often political dissidents, were shipped to Australia.

Women remained scarce on that continent, so during the potato famine of the 1840s, Britain sent more than 4,000 orphaned Irish teens as bride material, “hordes of useless trollops,” the Melbourne Argus sneered. Many married and began families. One of them became the great-great-grandmother of actress and singer Mandy Moore.

Famine refugees make up many of modern Irish-Americans’ ancestors. Once the grateful immigrants landed in America, they dug coal mines and laid railroad track. They doused fires and pounded beats. Some, with the pluck of the Irish, rose to the top. Both John Fitzgerald Kennedy and Joseph Robinette Biden came from families that fled the Great Hunger.

Although the Irish diaspora may have been a tragedy for Ireland, it became a boon for America. And the U.S. knew the value of a good story. When, on Jan. 1, 1892, the first ship landed at the new Ellis Island, immigrants rushed to step foot in America. A “burly German had one foot on the gangplank, when an Irishman named Mike Tierney” pushed him aside, paving the way for a teen and her younger brothers.

Pretty Annie Moore, 17, of Cork City, became “arguably the most famous emigrant in American history,” Bunbury writes.

She was given a $10 gold piece and as newspapers reported, “set free in the land of opportunity.”

Millions would follow in her footsteps.

They still do.

Jacqueline Cutler writes for the New York Daily News.