Obviously being able to read previously unintelligible writings was quite the incredible coup for Egyptology and expanded the scope of what could be studied, and knowledge of Ancient Egypt unimaginably. But that's not really what I mean. I'm more thinking about what the extent of knowledge was prior to the discovery of the Rosetta Stone, and how much of that remained valid, how much had to be seriously reevaluated, and how much was tossed out as straight up wrong - and of course, how much we knew at all! I presume sources were limited to Greek/Roman texts, and the Bible too perhaps, so just what did we know!?
To call the decipherment an "incredible coup" still feels like a bit of an understatement. It's truly impossible to overstate the importance of the Rosetta Stone to the field of Egyptology. It would not be inaccurate to say that the decipherment was the prime mover of the entire field.
Of course the Rosetta Stone didn't appear out of thin air. Napoleon's invasion of Egypt at the very end of the 18th century brought with it a team of academics, who were tasked with studying and documenting this "lost" civilization.^1 They produced the monumental Description de L'รgypte^2, including 10 elephant and 3 double-elephant-folio volumes with detailed engravings of buildings and facsimiles of Egyptian texts. I recently had the pleasure of leafing through one of the volumes in the Met's rare-book collection, and I was thoroughly impressed with the quality of the work. The Egyptian texts in the facsimiles and engravings are perfectly legible, despite being produced by people who didn't know how to read them (which is very rare, most depictions of hieroglyphs by non-specialists are bastardized to the point of illegibility). The accuracy and attention to detail of these volumes is legendary, so they naturally provided the basic material for Egyptological research. Napoleon's military campaign also saw the discovery of the Rosetta Stone in 1799, followed quickly by the distribution throughout Europe of prints produced by inking the stone itself. It was one of these prints that provided the source for Champollion's decipherment 23 years later. Egyptology was born of Napoleon's invasion of Egypt.
But the decision to bring scientists on a military expedition didn't arise out of thin air either. The political purpose of the invasion was control of the Suez, so there was no clear military need to document the entire country. The motivation for this part of the expedition was truly scientific (ignoring the obvious moral contradiction of invading a country in order to study it). Egypt was a popular subject of curiosity and speculation for centuries in Europe. With the Renaissance came a renewed interest in classical knowledge, and with that came the popular belief that Egypt was the ultimate source of European civilization, a view derived from that of the ancient Greeks. Egypt is also frequently mentioned in the Bible. The Hebrew of the Old Testament even includes quite a few Egyptian words, such as the Hebrew word for "Nile", ืืืจ, which is the Egyptian word for "river". (It's fun to imagine a Hebrew-speaking visitor to Egypt 3,000 years ago asking a native Egyptian: "What do you call this?" and the Egyptian responding simply: "river".) Finally, aegyptiaca were nearly as ubiquitous in Europe as they are today. Rome was already filled with the Egyptian obelisks that had been stolen centuries before by Roman emperors. The image of ancient Egypt was on people's minds. They wanted to know more, but the only way to learn more at the time was to go to Egypt and collect data.
With so much curiosity and so little information, it was only natural that some people would try to work things out on their own. Perhaps the most famous example is Athnasius Kircher's Oedipus Aegyptiacus, which is largely a work of speculative nonsense.^3 It was rooted in many other things, especially Horapollo's much earlier Hieroglyphica, which was also largely a work of speculative nonsense.^4 Pretty much everything that comes between classical authors and the decipherment is eloquently-written nonsense.
What is most interesting about all of these pre-decipherment works is that they are not always entirely wrong. They often have this "stopped clock" quality of being occasionally, accidentally right about a thing or two. For instance, Horapollo claims that ๐ means "eternity" because this species of snake is immortal. This seems vaguely insane until you unpack the ideas at the heart of it and relate them to the known facts. For starters, the Egyptian word ๐๐๐ฟ does mean "eternity". It has nothing to do with the animal itself, but depends on the simple coincidence of the phonetic values in the Egyptian words for "viper" and "eternity". ๐ is a phonetic symbol, it works more or less like the letters of our alphabet. Unlike our alphabet, ๐ has not evolved into an arbitrary shape, but retains the shape of the word from which its phonetic value originally derived. (This is occasionally true of our alphabet as well even if you didn't notice it before, you can still see the ox head in A if you flip it upside down: โ = ๐พ.) So the word for eternity has nothing to do with snakes except for their coincidental phonetic similarity in the Egyptian language, but the idea that certain sorts of snakes are immortal was very common (for example, it appears also in the Epic of Gilgamesh^5). It's probably a widespread bit of folk wisdom based on the observation that snakes shed their skin. By continually renewing themselves, perhaps snakes can live forever. It's not true of course, but it's not as absurd as it sounds at first. People today routinely make the same claim about lobsters (also false).
So a lot of people were curious about Egypt before the decipherment. Some people even thought that they knew something about Egypt, though they really didn't. Everything they knew was too wrapped up in confusion and uncertainty to be of any value. The greatest takeaway for me from all of this is how certain they were, despite being almost entirely wrong. It's easy to imagine Kircher and Horapollo asserting their beliefs with the same misplaced confidence of a modern academic, insisting that anyone who disagrees with them must be an utter fool. There's a comfortable uniformity in this element of human nature, alongside an excellent warning about proof, certainty, and the importance of getting good data. As a data scientist and egyptologist, I routinely experience the joy of trying to convince people who already know this history that collecting data is as valuable to scholarship as reasonably-informed speculation. I almost never succeed. Some things never change.
Edit: Added some notes and links.
