There are any number of historians and prelates abroad — and a very large number of scientists — who still today, on hearing the word “Lisbon,” instinctively think of a date rather than a place. To them, it is a word that signifies November 1, 1755 — All Souls Day, by some calendars — and it is remembered by them all as the moment when mankind suddenly began to come to its senses.

For as Nicholas Shrady remarks in “The Last Day” (Viking, 240 pages, $25.95), his admirable and perfectly-paced account of the earthquake which struck Iberia and North Africa with such haunting and ghastly consequences on that day, everyone “from staunch clerics to enlightened philosophers were compelled to re-examine their most cherished dogmas.”

So far as matters affecting the planet were concerned, after 1755 it was no longer entirely reasonable for intelligent men to believe that a supernatural God was in charge of all Earthly events. What happened that fateful morning was to a small but growing corps d’elite at last amenable to rational explication, and was not ascribable solely to the divine exercise of retributive Fate.

Lisbon was in consequence a turning point, a watershed — the kind of occasion of which a latterday Malcolm Gladwell might make much. Except that this was not a little thing that made a big difference; this was a very big thing that made quite a gigantic difference.

And Mr. Shrady describes the event itself both vividly and lucidly. So fervently God-fearing was the Portuguese capital’s population — with its people made fearful by the vicious wrath of the Inquisition — that an immense number of its quarter million citizens were in church that Saturday morning. In the basilica of São Vicente de Fora, packed with the pious, the choir was just beginning the introit when, at 9:40 a.m., “the whole church began to pitch and sway like a ship tossed in a tempest.” It was the Apocalypse, the congregation cried, and on rushing outside found that “whole blocks of houses had been reduced to rubble; chasms had swallowed lanes … landslides had smothered valleys, carriages lay wrecked, their horses withering in agony.”

It was indeed a temblor of titanic proportions, three mighty convulsions lasting more than four minutes, with its lethal effects extending as far south as Agadir in Morocco (which lost thousands in a similar event in 1960), and with tsunamis adding to the mayhem. One hundred thousand people died in the convulsion, which remains the most catastrophic of all natural events in European history.

But it is the reaction to the earthquake, rather than the event itself, that remains today so fascinating. For until the year 1755, all of the terrors that had been visited on humankind by nature — earthquakes, eruptions, floods, plagues, and storms — were said, unequivocally, to be the work of an angry God, with man paying the price for his manifold sins and wickedness.

It had been true for hundreds of years before, and it was initially true in Lisbon: A rabble-rousing Catholic obscurantist named Gabriel Malagrida caught the mood of the moment by wandering around the wrecked city proclaiming just this message: “Learn, O Lisbon,” he said,

that the destroyer of our houses, palaces, churches and convents, the cause of death of so many people and the flames that devoured vast treasures, are your abominable sins, and not comets, stars, vapors and exhalations, and similar natural phenomena.

The degree to which this advice was heeded remains a subject of debate. Some texts say that, as a response to the earthquake, many heretics — for which we should read “Protestants” — were burned to death, for this was a time when the auto-da-fé was still a popular persuasive tool. Others say that the Portuguese Secretary of State, Sebastião Carvalho, who managed the eventually highly efficient cleanup (FEMA could well have used a man like Carvalho after Hurricane Katrina), was sufficiently enlightened to downplay the need for penitence, and instead focused on burying the dead and feeding the living, which has since become the mantra of all emergency responders.

Mr. Shrady wisely skirts wide of this particular row, but writes at length about the most famous literary inheritor of the catastrophe: Voltaire. For it was Voltaire who employed the disaster to advance the cause of the Enlightenment, at the expense of prevailing Christian dogma. It was asinine, he insisted, for humankind to assume that God was behind this particular event, or any other: “What a game of chance life is!” he wrote, in a letter to a friend the day after hearing of the disaster.

What will the preachers say — especially if the Palace of the Inquisition is left standing! I flatter myself that those reverend fathers, the Inquisitors, will have been crushed like other people. That ought to teach men not to persecute men: for while a few sanctimonious humbugs are burning a few fanatics, the earth opens up and swallows all alike.

He then wrote “Candide,” satirizing most mercilessly these fanatics and fundamentalists, and lampooning the lunatic notion that, thanks to God, mankind inhabits the best of all possible worlds: If such a world encompassed events like Lisbon, he had Candide wonder, then, pray, what of the others?

After 1755, and in part because the new mood of skepticism afforded by such writers as Voltaire, scientists began to creep out of the woodwork, cautiously challenging the protectorates of the priesthood, and started to investigate the causes of allegedly divine events that had scourged the world for so long.

But the march of science took time: Fanatical Muslims still believed an angry Allah to be at work in causing Krakatoa to erupt so violently in 1883, and many Christian fantasists went on to claim that the San Francisco earthquake of 1906 was also a punishment for human wickedness. Mr. Shrady even quotes the late Catholic archbishop of New Orleans, Philip Hannan, claiming in the wake of Katrina that “the Lord has a right to chastisement,” and that the disaster had been a kind of divine punishment for Cajun vice. Some primitive attitudes soldier on.

Mr. Winchester is the author of “The Professor and the Madman,” “Krakatoa: The Day The World Exploded,” and “A Crack in the Edge of the World.”