In July 1799, during Napoleon Bonaparte's military invasion of Egypt, a group of French soldiers accidentally made a groundbreaking archaeological discovery. While working to strengthen the defenses of a sunbaked fort near the Nile Delta town of Rosetta (modern-day Rashid), they knocked down a wall and unearthed a 44-inch-long, 30-inch-wide chunk of black granodiorite.

It wasn't unusual for the French troops to stumble upon Egyptian relics, but this particular slab caught the attention of Pierre-Francois Bouchard, the engineer in charge. When, upon closer inspection, he noticed that it was covered in ancient text, he halted demolition and sent word to his superior officer. Experts would soon confirm that the stone contained writing in three different scripts: Greek, demotic, or everyday, Egyptian and hieroglyphics.

Almost immediately, Bonaparte remarked on the stone's potential. "There appears no doubt that the column which bears the hieroglyphs contains the same inscription as the other two," he said before the National Institute in Paris that autumn. "Thus, here is a means of acquiring certain information of this, until now, unintelligible language."

While the French soldiers couldn't have known it at the time, the "Rosetta Stone" they pulled from the rubble would trigger one of history's great intellectual odysseys. The meaning of Egyptian hieroglyphics had been lost since the dying days of the Roman Empire, but with its triple inscription, the stone offered scholars a chance to decipher the ancient symbols once and for all—making the find the key to this remarkable period in history. Yet it would take decades, and the work of two brilliant scholars, to unlock the stone's secrets.

Soon after its discovery, the Rosetta Stone was already the subject on international intrigue when British forces seized it in 1801 after defeating the French in Egypt. By then, several casts and copies of its text had been made, allowing researchers across the globe to begin experimenting with potential translations. The first and easiest step, deciphering the Greek text, revealed that the Rosetta Stone contained a relatively mundane Egyptian decree praising the 2nd–century B.C. boy-king Ptolemy V Epiphanes. A rudimentary translation of the demotic text (a script rendering of the everyday Egyptian language) followed shortly thereafter. But when linguists tried to tackle the portions written in hieroglyphics, most were left scratching their heads.

Thomas Young. (Credit: Pictorial Press Ltd/Alamy Stock Photo)

A clear understanding of how the ancient script functioned would ultimately take 20 years and involve two of the early 19th century's greatest minds. The first major discoveries came courtesy of Thomas Young, a British polymath who had previously made contributions to physics, optics, medicine and mathematics. In 1814, the 41-year-old began tinkering with a copy of the Rosetta Stone's inscriptions during what he described as "the amusement of a few leisure hours." Piggybacking off previous research by Swedish scholar Johann Akerblad and Frenchman Silvestre de Sacy, Young eventually focused on the text's "cartouches"—ovals that enclosed certain groupings of hieroglyphic script. After concluding that the cartouches were used to denote royal names, he matched one of them to the name "Ptolemy" in the Greek text and identified the phonetic properties of several hieroglyphic signs.

Young's other inroads concerned the demotic Egyptian script. According to author Andrew Robinson's book Cracking the Egyptian Code, Young proved that demotic script derived from hieroglyphics and contained individual phonetic letters as well as ideographic symbols. Demotic "was neither a purely conceptual or symbolic script, nor an alphabet, but a mixture of the two," Robinson wrote. Crucially, however, Young did not apply these same revelations to hieroglyphics. Like most scholars at the time, he subscribed to the belief that hieroglyphics were almost entirely symbolic, and he theorized that the script only had phonetic properties when spelling out foreign names.

Young eventually set his aside his Rosetta Stone research in 1819 and took up other intellectual pursuits. Around that same time, the French scholar Jean-Francois Champollion began to give the ancient slab his full focus. Brilliant, eccentric and prone to occasional fainting fits, Champollion was a former child prodigy who had mastered half a dozen languages by his teens. He also harbored a lifelong fascination with the mysteries of Egypt. "I want to make a profound and continuous study of this ancient nation," he vowed in an 1806 letter.

Jean-Francois Champollion. (Credit: Paul Fearn/Alamy Stock Photo)

In 1821, Champollion settled in Paris and began a personal quest to decipher the Rosetta Stone. The 30-year-old benefited from Young's earlier research—in particular his work on the cartouches—but he also had the advantage of being fluent in Coptic, a language that was descended from ancient Egyptian. Following months of painstaking labor, Champollion succeeded in identifying some of the phonetic hieroglyphic signs used in foreign royal names such as "Cleopatra" and "Ptolemy." He then applied the signs to the names in the cartouches found on the Rosetta Stone and elsewhere, using the discoveries from each new translation to fill in the gaps on the others.

Champollion's cross-referencing technique allowed him to develop a working hieroglyphic alphabet, but his true eureka moment came in September 1822, when he realized that the hieroglyphic spelling of "Ramses"—a traditional Egyptian name—was made up of symbols that all corresponded to spoken sounds. By applying these same phonetic symbols to other words on the Rosetta Stone that weren't enclosed in cartouches, he made a discovery that had eluded all previous scholars: Rather than being a purely symbolic script, hieroglyphics included both conceptual symbols and phonetic signs.

Depending on their context, the symbols in the script could represent entire words and phrases or individual components corresponding to the sounds of spoken language. According to legend, Champollion was so floored by his revelation that he raced to his brother's office and screamed, "I've done it!" before immediately fainting.

Notes on hieroglyphs in Jean-Francois Champollion notebook, c1806-1832. (Credit: Art Media/Print Collector/Getty Images)

Once he hit on its phonetic properties, Champollion was able to begin unraveling the mysteries of hieroglyphics. Following several years of additional study, he published research that outlined the underlying principles of the Egyptian writing system. Armed with his new knowledge, he made a pilgrimage to Egypt, where he became the first known person in more than 1,400 years to read the inscriptions on ancient Egyptian tombs and monuments. "Before Champollion, the ancient voices from the ancient world that could be heard were from the Greece, Rome and the Bible," historian John Ray wrote in his book The Rosetta Stone and the Rebirth of Ancient Egypt. "Now the Egyptians were beginning to speak with their own voice."

Champollion died in 1832 at the age of just 41. Today, he's credited with creating the field of modern Egyptology by giving scholars access to ancient Egyptian literature and culture.

Just how much of a debt Champollion owed to Thomas Young's earlier scholarship has long been a matter of debate. French researchers have traditionally tended to trumpet Champollion's work, while British scholars highlight Young's earlier discoveries. Still, most modern historians give the Frenchman the lion's share of the credit. "Any decipherment stands or falls as a whole," the Egyptologist Richard Parkinson wrote, "and while Young discovered parts of an alphabet—a key—Champollion unlocked an entire written language."

Equally important was the Rosetta Stone itself. By allowing scholars to compare hieroglyphics to known languages, it helped them decode a lost language. For more than 200 years, the original stone has been housed in London's British Museum, where it receives millions of visitors annually. As the artifact responsible for rescuing ancient Egypt from the mists of time, the 2,200-year-old slab is often listed among history's most important archaeological discoveries—the key that unlocked the secrets of a civilization.