Thomas Cahill, a multilingual scholar who wrote a surprise 1995 best seller demonstrating to the world how a small band of Irish monks collected and protected the jewels of Western civilization after the fall of the Western Roman Empire, died on Oct. 18 at his home in Manhattan. He was 82.

His wife, Susan Cahill, said the cause was a heart attack.

“How the Irish Saved Civilization: The Untold Story of Ireland’s Heroic Role From the Fall of Rome to the Rise of Medieval Europe” was not Mr. Cahill’s first book. But it immediately established his reputation as one of the country’s great writers of popular history.

In the book, he argued that even though the Romans never conquered remote, rural Ireland, Christianity did — and that as the continent descended into darkness and anarchy after the last Western Roman emperor was deposed in 476, its isolation became its advantage.

Living in relative peace, Irish scholars transcribed countless pagan and Christian texts, maintained a semblance of literary culture and, perhaps most important, developed a lively, life-affirming Christianity that later seeded the revival of the Roman Catholic Church in Western Europe.

Five publishers rejected Mr. Cahill’s proposal before the editor Nan A. Talese, at Doubleday, snapped it up in 1991. To many would-be publishers, the title sounded like a bunch of blarney — even in the early 1990s, many people still considered Ireland a conservative backwater and a cultural appendage to Britain.

That image changed rapidly in subsequent years. Ireland’s economy began to boom, the violent conflict in Northern Ireland known as the Troubles was settling down, and Irish culture was suddenly everywhere. The near-simultaneous appearance of “How the Irish Saved Civilization” and “Angela’s Ashes,” a 1996 memoir about growing up Irish American by Mr. Cahill’s friend Frank McCourt, was a coincidence, but their immediate and lasting popularity certainly was not.

“How the Irish Saved Civilization” spent nearly two years on The New York Times’s best-seller list and sold some two million copies.

Mr. Cahill’s success was about more than good timing. He was multilingual (he knew Latin, ancient Greek, French, German and Italian) and had a firm mastery of both primary sources and the academic scholarship around them. He was also a fluid, engaging writer, able to bring entertainment as well as erudition to the page.