Some 3.5 million Italians live in the shadow of Mount Vesuvius. Much of Naples is built on its green slopes.

Their idyllic life is built on the soil of one of the most cataclysmic, chilling disasters in human history: the destruction of Pompeii.

In a.d. 79, Mount Vesuvius erupted. Searing, toxic clouds of superheated gas and fire charged down the slopes at more than 300 miles per hour. Ash blackened the sun; day turned into night. Pyroclastic flow buried the Italian city of Herculaneum. For the inhabitants of Pompeii, a worse but equally inescapable fate awaited.

“[D]arkness fell, not the dark of a moonless or cloudy night, but as if the lamp had been put out in a closed room,” wrote Pliny the Younger, who witnessed the cataclysm from across the Bay of Naples. He described a strange cloud that looked like a pine tree shooting out of Vesuvius.

What he was seeing was a column of volcanic gas, magma bombs and cinders shooting skyward at supersonic speeds out of the mouth of the volcano. As the particles spread and cooled, they began to rain down—forming the characteristic Italian Stone Pine tree shape, or mushroom cloud.

The unfortunate inhabitants of Pompeii who did not flee at the first rumbles were poisoned and buried by the fallout.

More than 1,900 years later, it is hard not to be moved by what archaeologists have found beneath the layers of cinders. It is far more than just the lifeless city that is frozen in time. The inhabitants’ ash-charred final moments of agony are preserved too:

A mother sheltering her infant. A father covering his son. A man pulling his coat over his mouth to breathe. A family fleeing for the harbor and a chance to escape only to be overcome by fumes. Lifeless bodies adorned in jewelry, their most prized valuables—but no amount of treasure could save them.

Death for these people came suddenly and catastrophically. Scientists say the first breath of the superheated gas would have vaporized the internal organs. For others hit by slightly cooler fumes, their charred forms remained to be buried—and hidden for the next 1,669 years.

One morning, Pompeii was a bustling, prosperous vacation destination. The next, it was empty, plain, wiped clean of life.

Today, on the very slopes where death and destruction rained down, a new modern metropolis stands. Not far from the beautifully constructed Roman frescoes and excavated bathhouses of Pompeii are grocery stores and nightclubs. New docks and harbors and a yacht club line the shores where merchant warehouses once stood.

Their presence is a monument to the unteachability of human nature.

To this day, Vesuvius remains one of the world’s most threatening volcanoes. It is alive. It shudders. It has erupted more than 30 times since destroying Pompeii. It killed 4,000 people in 1631. It killed 2,000 more in 1906. Its latest eruption was 1944.

City planners know the mountain will erupt again—it is just a matter of time. They say 600,000 people live in the most dangerous “red zone.”

Contingency plans require up to 20 days for full evacuations. People know this. They also know that if the volcano erupts again, they probably won’t escape.

Although monitoring devices are in place to warn of the volcanic activity, “if there is a major eruption with little warning and the winds are blowing toward Naples,” says Field Museum geologist Philip Janney, “you could have tremendous loss of life.”

How weak is human nature. Failing to learn from history, we become complacent—dulled to danger. Even history that is preserved before our eyes—the bodies of people incinerated while fleeing the very ground we now live on—can become remote and unreal.

It is alarmingly easy to “put far away the evil day.” In a prophecy where He described what the world would be like before His Second Coming, Jesus Christ warned against complacency (Matthew 24:36-39). “Watch therefore,” He continued: “be ye also ready: for in such an hour as ye think not the Son of man cometh” (verses 42, 44).

When we watch the world around us, we need to actively work not to become numbed. We must not let ourselves begin to think that we are living in normal days—that what is happening has always happened. Extraordinary, unprecedented, earthshaking events are making headlines with increasing rapidity. Prophecy is being fulfilled like never before. The ground is rumbling. Don’t ignore it. Don’t become desensitized. Realize just how quickly the evil day could be here.

“[T]ake heed to yourselves, lest at any time your hearts be overcharged with surfeiting, and drunkenness, and cares of this life, and so that day come upon you unawares,” Christ warned. “For as a snare shall it come on all them that dwell on the face of the whole earth” (Luke 21:34-35).

Christ gave this warning so you could be among the few who escape the terrible events soon to strike (verse 36).

But like the residents of Pompeii and Herculaneum, most will not escape the coming world explosion. People remain confident in their own power. They deceive themselves and hold fast to an illusion of security. Meanwhile, this world hurtles toward the prophesied days of reckoning at pyroclastic-flow speeds.

“For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape” (1 Thessalonians 5:3).

Flee complacency—before it is too late.