The cause was a heart attack, said his wife, author Susan Cahill. Mr. Cahill had heart disease and suffered a stroke in 2017, she said, but had continued to work in recent years.
A devoted student of ancient Greek and Latin, the Jesuit-trained Mr. Cahill worked in journalism and publishing before becoming a full-time author. Capitalizing on the phenomenal success of “How the Irish Saved Civilization” (1995), which spent almost two years on the New York Times bestseller list, he wrote five more books about key moments in the development of Western civilization, drawing from scholarly research and primary sources while crafting books that were as entertaining as they were erudite.
Mr. Cahill was not a professional historian, and was criticized at times for making far-reaching claims without ample evidence. Yet his work was praised for transporting readers into the distant past, and for bringing history alive without getting bogged down by fusty details.
Scholars, he once told the Philadelphia Inquirer, “tend to be extremely cerebral and go toward ‘what’s the philosophical structure here, or what’s the ideological structure?’ They miss the tears and the laughter, the blood, the sweat, all those things that actually put us in touch with these people of the past.”
Mr. Cahill was working as Doubleday’s director of religious publishing when he wrote “How the Irish Saved Civilization,” inspired in part by a trip to Ireland 20 years earlier. The book told the lively — but relatively little known — story of how 5th-century Irish monks copied down classical texts onto sheepskin, rescuing works of literature and philosophy that were being destroyed by Germanic invaders after the collapse of the Roman Empire. It was, Mr. Cahill wrote, Ireland’s “one moment of unblemished glory.”
The book sold some 2 million copies and was a jubilant affirmation of Irish culture and history after years in which the country’s role in world affairs was often derided or ignored. As Mr. Cahill put it, the Irish would generally be considered “a very uncivilized people to save civilization.”
His book offered a corrective to that view while introducing characters including Augustine of Hippo (“almost the last great classical man”), Saint Patrick (“the first human being in the history of the world to speak out unequivocally against slavery”) and the warrior queen Queen Medb of Connacht.
“His writing is in the great Irish tradition he describes: lyrical, playful, penetrating and serious, but never too serious,” wrote New York Times book critic Richard Bernstein. “And even when his conclusions are not entirely persuasive — they do in places hang on rather slender reeds of evidence — they are always plausible and certainly interesting.”
Mr. Cahill went on to write six total volumes in what he called his “Hinges of History” series, an idiosyncratic survey of Western civilization in which he aimed to offer “a narration of how we became the people that we are.” His follow-up, “The Gifts of the Jews” (1998), was a breezy retelling of biblical history that credited the Jewish people — “a tribe of desert nomads” — with pioneering the concept of individuality, not to mention the idea of the weekend. To research the book, he spent a summer learning Hebrew, studied at the Jewish Theological Seminary in New York and traveled to the Middle East to visit Old Testament landmarks.
“I tried for several years to live with the people of the Bible,” he told the Los Angeles Times. “Finally, I could see Abraham’s tent in the desert heat.”
Mr. Cahill later explored the life and legacy of Jesus (“Desire of the Everlasting Hills”), the role of art and war in ancient Greece (“Sailing the Wine-Dark Sea”), the cultural and political advances that occurred in the so-called Dark Ages (“Mysteries of the Middle Ages”) and the rise of modern individualism during the Renaissance and Reformation (“Heretics and Heroes”).
His books were filled with lengthy quotes from primary sources as well as colloquial asides and comparisons to modern life. A letter from the Middle Ages was “as full of catty innuendo as the dialogue from an episode of ‘Desperate Housewives,’ ” while the Greek city-state of Sparta was “the North Korea of its day.” In ancient Greece, he wrote, “the harder the pecs and the tighter the buns the more spiritual you were.”
“What academic writers forget is that everyone on Earth buys books for diversion, or entertainment,” he told the Associated Press in 2006. “Yes, they want to learn things, but they also don’t want to be bored to death while they learn those things.”
Thomas Quinn Cahill was born in the Bronx on March 29, 1940. His parents were the children of Irish immigrants, and he grew up hearing songs and stories about life in Ireland from his mother, a homemaker. His father was an insurance executive.
Mr. Cahill earned a scholarship to Regis High School, the elite Jesuit private school on Manhattan’s Upper East Side, where he was introduced to the work of Plato and Augustine at age 14. He went on to major in classical literature and medieval philosophy at Fordham University, receiving a bachelor’s degree in 1964, and studied for the priesthood before deciding against it.
At Columbia University he studied film, receiving a master’s degree in 1968. That was a dead-end as well: Filmmakers, he decided, “either starve or have rich daddies and connections.”
Going into journalism and publishing, he worked as an advertising director at the New York Review of Books and an education correspondent at the Times of London. He also wrote book reviews for the Los Angeles Times and taught at schools including Seton Hall University, Queens College and Fordham.
With the former Susan Neunzig, whom he married in 1966, he published his first book, the anthology “Big City Stories by Modern American Writers,” in 1971. They later started a mail-order book catalogue and spent a year in Ireland researching their second book, “A Literary Guide to Ireland” (1973).
For decades, Mr. Cahill kept his idea for an Irish history book in his back pocket, unsuccessfully pitching it to five major publishers before meeting editor Nan Talese, who signed on to the project after they met at a sales conference in 1990.
By then, Mr. Cahill was the director of religious publishing at Doubleday, releasing titles that included the six-volume “Anchor Bible Dictionary,” which became a crucial resource for his subsequent history books. He also published an English translation of “Eunuchs for the Kingdom of Heaven,” by German theologian Uta Ranke-Heinemann, about women, sexuality and the Catholic Church.
Mr. Cahill told the Irish Times that when he saw the dour cover art that had been planned for the book, he went to Doubleday’s art department and said, “Give me something that’ll give a bishop apoplexy at breakfast.” The resulting book was published with a sensual illustration showing a woman in silhouette, and was attacked by influential Cardinal John J. O’Connor, who declared that Doubleday was a “purveyor of hatred and scandal and malice and libel and calumny.” (Mr. Cahill said he and other editors felt “defamed” by O’Connor, but noted that the cardinal’s comments seemed to have the opposite of the intended effect, boosting the book’s sales.)
After the success of “How the Irish Saved Civilization,” Mr. Cahill quit his day job, aiming to write a new book every two years. His later works included “Pope John XXIII” (2002), a short biography for the Penguin Lives series, and “A Saint on Death Row” (2009), about Dominique Green, a Texan who was convicted — wrongly, in Mr. Cahill’s eyes — of fatally shooting a man during a robbery outside a convenience store. Green was executed in 2004, after Mr. Cahill unsuccessfully sought to clear his name.
In addition to his wife, Mr. Cahill’s survivors include their two children, Kristin Cahill Iñiguez and Joseph Cahill; three sisters; and four grandchildren.
Mr. Cahill was skeptical of institutional religion, saying that he found “churches often get in the way” of faith. But for many years he led a prayer group in New York, taking time off from his writing to read bedtime stories to children with HIV.
“We’re just a bunch of middle class people,” he told the New York Times in 1998. “None of this is earthshaking or monumental. It seems extremely minor, but everything is minor in a way.
“You know the famous response of Mother Teresa when someone asked her how she did it? ‘One by one.’ I think that is always the response.”