Humans have documented earthquakes for nearly 4,000 years. Of those recorded, the deadliest occurred in China. On January 23, 1556, a powerful quake rocked the province of Shaanxi and the neighboring province of Shanxi, killing an estimated 830,000 people.

Historical records often refer to the 1556 Shaanxi earthquake as the Jiajing Great Earthquake because it occurred during Emperor Jiajing’s reign in the Ming dynasty. The approximate death toll comes from local annals that also tracked 26 earthquakes in the region. In those records, the earthquake is starkly different from others: they describe leveled mountains, floods, fires that burned for days and a drastically altered landscape. The annals estimated that some counties lost about 60 percent of their population.

Even though the death toll is in question, the Shaanxi earthquake is considered the deadliest earthquake because its casualties are much higher than any other disaster. (The second deadliest recorded earthquake next to Shaanxi was the 2004 earthquake and tsunami in the Indian Ocean that killed an estimated 230,000 people across Indonesia, Thailand, Sri Lanka and India.)

After the development of the Richter scale in the 1930s, scientists theorized that the Shaanxi earthquake was likely between 8.0 to 8.3 in magnitude—not the strongest ever recorded, but no less destructive. The most powerful earthquake recorded on the Richter scale was the 9.5-magnitude Valdivia Earthquake that struck Chile in 1960, according to the U.S. Geological Survey (USGS). The seismic event created a tsunami which together killed an estimated 5,700 people. The 2004 Indian Ocean tsunami registered a 9.3 magnitude.

Without being the strongest recorded earthquake, Shaanxi's high death toll likely resulted from the destruction of the area's densely populated communities and poorly-constructed stone buildings. According to local records, the people of the Shaanxi and Shanxi provinces responded to the natural disaster by rebuilding in ways that would lessen the impact of future earthquakes. Since the earthquake toppled so many stone buildings, communities rebuilt with softer materials like bamboo and wood, which were more resistant to tremors and would cause less damage if knocked down again.

The scholar Qin Keda, who survived the earthquake, wrote about his experience and came up with safety tips for people to follow in the event of another disaster. “At the very beginning of the earthquake, people indoors should not go out immediately," Keda wrote. "Just crouch down and wait for chances. Even if the nest is collapsed, some eggs in it may still be kept intact.”

Qin Keda’s advice to stay indoors mirrors the USGS's advice. In a section of its website titled “What should I do DURING an earthquake,” the USGS says that if you are already inside during an earthquake, it is not safer to head for the door. Running during an earthquake is very dangerous, and being inside can protect you from flying debris.

The USGS advises (in all-caps) that if an earthquake happens while you are indoors, you should “DROP, COVER, AND HOLD ON”—essentially the same advice that Qin Keda gave over 450 years ago.