Before chemist Claude-Louis Berthollet's realization, the concept that chemical reactions could be reversible wasn't universally accepted.

However, Berthollet found strong evidence to support the idea while studying the salt deposits in the lakes of the Natron Valley.

Natron, a naturally occurring salt, covered the limestone in the lakes. Ancient Egyptians had used the substance to preserve mummified bodies because it absorbed moisture and dissolved fat.

Berthollet observed that the limestone, which contained calcium carbonate, chemically reacted with salt, aka sodium chloride, to produce natron, made of sodium carbonate.

In laboratory conditions, chemists knew that the exact opposite reaction was possible, which led Berthollet to reasonably conclude that chemical reactions were reversible and that heat and different amounts of a substance could determine which way the reaction went.

In Napoleon's time, archaeology wasn't yet a formal science. Most savants had little experience with artifacts. Sand still buried some temples that had yet to be excavated.

Dominique-Vivant Denon, an artist and writer, was awed by the ancient monuments he saw. He went back to France with Napoleon and quickly published a book with his descriptions and drawings, "Travels in Upper and Lower Egypt."

At the time of Napoleon's invasion, travelers had long known of Alexandria, Cairo, and other parts of Lower Egypt. The Great Pyramids and Sphinx were famous. But Upper Egypt wasn't as well known.

That changed when the savants arrived. "The whole army, suddenly and with one accord, stood in amazement... and clapped their hands with delight," Denon later wrote.

His drawings and descriptions of the temples and ruins at Thebes, Esna, Edfu, and Karnak proved immensely popular. Many were depicted in fashionable paintings and inspired decor trends.

Since he'd had to capture everything in short bursts of time, Denon had pushed for two commissions of savants to return and better document the monuments.

Napoleon's architects and engineers made careful drawings and took measurements of a large number of monuments. Others attempted to measure the pyramids. (Napoleon never shot them with cannons, in case you were wondering.)

Just 21 and a botanist by training when he arrived in Egypt, Jules-César Savigny collected invertebrates like worms, bees, spiders, snails, and flies. He also took specimens of starfish, coral, and sea urchins.

When he was back in France, Savigny needed to organize the 1,500 species of insects he'd brought from Egypt. There didn't yet exist a systematic way to distinguish one species of moth or butterfly from another. So Savigny invented one.

Surprisingly, the bugs' mouth parts had sufficient differences to allow Savigny to separate them into species. He pored over the tiny jaws of the insects. He drew over 1,000 images of specimens, some of which were only a centimeter long.

Savigny applied the same rigor to arachnids, worms, and other animals that lacked backbones. Some of his classification methods are still in use today.

Etienne Geoffroy Saint-Hilaire was convinced there were two species of crocodiles in the Nile.

Like Savigny, Geoffroy was a prolific collector. While in Egypt, he studied bats, mongooses, tortoises, and more.

One reason Geoffroy was able to dissect and stuff so many specimens was he had purchased an 11-year-old enslaved boy, whom he trained to help with his work.

Geoffroy closely examined so many different kinds of animals that he started to see patterns between even very different species. It led to his theory of a "unity of plan" or "unity of composition" a kind of quasi-evolutionary idea that Charles Darwin would reference decades later.

Geoffroy's theories often irritated his fellow naturalists. That includes when he attempted to demonstrate a mummified crocodile he'd taken from Egypt represented a separate species.

Its jaw was completely different from the Nile crocodile, Geoffroy said. Plus, it was less aggressive. One had even been on display in Paris. "It took pleasure in being patted; and anyone might, without the least danger, open its mouth, and place his hand between its teeth," according to one account.

His colleagues didn't believe him. However, over 200 years later, biologist Evon Hekkala and a team of researchers analyzed the DNA of modern crocodiles and some of Geoffroy's mummies to confirm his suspicions. Indeed, they showed two separate species swam in the Nile: Crocodylus niloticus and Crocodylus suchus.

The French physicians who accompanied Napoleon encountered unfamiliar illnesses in Egpyt. One disease that traveled with them back to Europe was something they called Egyptian ophthalmia. Now known as trachoma, it can cause itchy, swollen eyes and lead to blindness.

It became so prevalent that physicians all over Europe started studying the disease. Geoffroy, who contracted it, was "totally blind" for weeks, he wrote.

Up to that point, ophthalmology wasn't a formalized branch of scientific research, but the race to find the origin of this disease laid the groundwork for its creation.

Eventually, British physician John Vetch realized the pus from an infected eye could spread the disease. Knowing it was contagious, Vetch developed methods of prevention and treatment that are considered milestones in the history of ophthalmology.

For centuries, no one could read hieroglyphs, the pictorial writing that covered many Egyptian monuments.

When the French found the Rosetta Stone during their invasion, they knew it could serve as a kind of translation key.

Deciphering hieroglyphs would allow scholars to read the writing on scores of other Ancient Egyptian texts and monuments.

In 1801, the British were negotiating for France's surrender. One stipulation was that the British would take the antiquities and the savants' collections, which included the Rosetta Stone.

Geoffroy told the British that the savants would "destroy our property, we will disperse it in the Libyan sands, or we will throw it into the sea" before they handed it over. They were allowed to keep their notes and collections. But not the slab.

Three texts were inscribed on the stone in Egyptian hieroglyphs, an Egyptian cursive script derived from hieroglyphs, and Ancient Greek. Since the three were identical, the Greek writing could help researchers decipher the hieroglyphs.

It took two decades for French scholar Jean-François Champollion to translate them. Champollion made use of a copy the French savants had taken of the slab and published.

The Rosetta Stone is currently in the British Museum. Egypt has been trying to get it back, calling it a "spoil of war."

When the savants returned to France, many worked on compiling the multi-volume book "Description de l'Égypte," which amounted to 7,000 pages encompassing what they'd seen and studied in Egypt.

To save some of the laborious work of engraving, engineer Nicolas-Jacques Conté created a machine that automated part of the process.

To print the hundreds of illustrations, engravers first had to transfer them to copper plates.

For plates with monuments, Conté's machine could engrave the sky in the background. The engraver could program it to create clouds as well.

What originally would've taken six to eight months could be completed in just a few days.

It was still a massive undertaking and considered to be the most ambitious work of France in the early 19th Century. The first volume wasn't printed until 1809. The final volume came out in the late 1820s, nearly a decade after Napoloen's death.

Many savants were tasked with documenting the natural history of Egypt. Mining engineer François-Michel de Rozière had the difficult job of describing the country's rocks and minerals.

Decades before Napoleon's invasion, many naturalists started adopting Carl Linnaeus' two-word system for naming plants and animals. But rocks and minerals lacked a similar widely accepted language.

To accurately capture the nuances of the granite or shells he saw, Rozière painstakingly described their textures, layers, and colors. One description referenced "transparent quartz, yellowish feldspath, and black schist."

He also understood the importance of including illustrations of the rocks, which made them much easier for other savants to identify. In the Description de l'Egypte, his fifteen plates contained over 100 colorful illustrations of porphyry, basalt, and other rocks and fossils.

Though Napoleon didn't use the geological knowledge his savants gathered in Egypt, some argue that his invasion spurred the creation of military geology. Soon, scientists were surveying unfamiliar terrain during campaigns and using their knowledge for engineering projects.

In the midst of his work on the Rosetta Stone, Champollion decried the removal of another piece of Ancient Egyptian history from the country.

During a quick visit to the Dendera temple, Denon had sketched the ceiling, where Ancient Egyptians had carved zodiac signs, Egyptian constellations, and other figures into the stone. Other engineers made more detailed drawings of the intricate design.

In 1821, a French expedition dynamited part of the temple and took the zodiac ceiling to France. Champollion worried the removal of the zodiac would lead to the "complete destruction" of the rest of the ceiling and stripped the artifact of important context.

French scholars debated whether they could use depicted features like eclipses to date its creation. At the time, no one knew exactly how far back in time human history stretched. Some estimated the zodiac was older than 5,000 years BCE. Others suggested more recent dates such as 800 BCE. Champollion thought deciphering hieroglyphics would offer a more reliable dating method than an interpretation of the ancient sky.

More recent dating techniques put the Dendera zodiac at around 50 BCE, around Cleopatra's era. One researcher called it "the only complete map that we have of an ancient sky" from that era. It remains in the Louvre Museum in Paris.

This story was originally published on December 2, 2023, and most recently updated on November 14, 2024.