Humans have been recording earthquakes for nearly 4,000 years. From the ones we know about, the deadliest by far happened in China in 1556 A.D. On January 23 of that year, a powerful quake rocked the province of Shaanxi as well as the neighboring province of Shanxi, killing an estimated 830,000 people.

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

Even though we can’t be certain of how accurate the estimate of fatalities was, Jiajing is still considered the deadliest earthquake today because its death toll is just so much higher than any other disaster. The closest in terms of casualties that we know of was the 2004 earthquake and tsunami in the Indian Ocean that killed an estimated 230,000 people across Indonesia, Thailand, Sri Lanka, and India.

Map displaying the propagation of seismic waves after the Sumatra quake at the Geo Science Center in Potsdam. (Credit: Michael Urban/AFP/Getty Images)

After the development of the Richter scale in the 1930s, scientists theorized the Shaanxi earthquake was probably between a 8.0 to 8.3 in magnitude—not the strongest one ever recorded, but certainly significant. The most powerful quake was the 9.5-magnitude Valdivia Earthquake that struck in Chile in 1960, according to the U.S. Geological Survey (USGS). That quake created a tsunami, which together killed an estimated 5,700 people. The 2004 Indian Ocean tsunami registered a 9.3 magnitude.

So if Jiajing wasn’t the strongest quake, why was it the most deadly? Likely, the high death toll resulted from a combination of densely populated communities and poorly-constructed stone buildings. According to the local records, the people of the Shaanxi and Shanxi provinces responded to the natural disaster by trying to rebuild in a way that would lessen the impact of future earthquakes. Since the quake had lethally toppled so many stone buildings, communities rebuilt with softer materials like bamboo and wood, which were more resistant to earthquakes and would cause less damage if they fell on you.

The scholar Qin Keda, who survived the earthquake to write about it, also came up with safety tips for people to follow in the event of another disaster. Headvised: “at the very beginning of the earthquake, people indoors should not go out immediately. 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 was correct. In fact, it mirrors the advice the USGS gives today. In a section of its website titled “Earthquake Facts & Earthquake Fantasy,” 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”—basically the same advice that Qin Keda gave over 450 years ago.