I think, as interesting as the question is, its a bit wonky to answer. You're really asking someone to prove the impossibility or something or concede that it is possible. Historians don't usually dabble in that, without any proof- whether it be written, archeological, or oral in nature- there is no way to give a clear answer or lay the foundation for one. All things are possible in some sense, but not always likely or probable.

For a large unknown empire (or empires) to have existed, we would need to ask ourselves, why did they not need writing? The fact is, an important technology for empire building is communication and writing is a par excellence the technology for communicating across space and time. So it would be hard to imagine the large self governing empire existing without effective communication technologies.

We would also want to ask, why is there no evidence? No material goods we have ever found, why did they not engage in megalithic architecture like most other societies? Where in the world did societies not engage in megalithic construction? Why? Could an empire have existed in those climates? Where was agriculture widespread enough that an empire could feed itself or afford to have people not engaged in food production? Maybe we could answer some of these, but ultimately the problem is we are starting with the answer we want and looking for evidence for it. That's not good science.

Like I said at the top, historians don't usually start out to prove something did not happen. If one sets out to prove that ancient empires existed before the creation of writing, then one will likely find evidence for it. Instead we should ask, what was life like before the invention of writing? How was human society organized in different places and at different times? Opening up the question for more potential possibilities allows one to conduct a more open research; rather than directly looking for proof that empires or something specific existed.

Conversely we could start with the question; when do empires begin to form? And then we might want to start first and foremost with what is an empire. What sorts of things do empires have in common? What alternative models of empire exist? Are there social organizations that resemble empire but don't fit the definition? From here maybe we could work back looking at already well studied societies - at this point though we're practically into anthropology. Yet it would be a useful tool to help us push back in time and understand the evolution of social governance into what might fit our label of empire.

Editing to add a couple notes:

• Thank you for the Gold! An unexpected treat.

• A lack of evidence is not itself substantial evidence. Again, why we don't try to prove a negative.

• There is no denial above that there are societies or even urban societies that we simply know nothing about and have never discovered. Whether they were an empire is likely a question on a different scale.

• Definitions are important. I was happy to see the queries about what an empire could be. This is usually how I start my semester with students. Definitions include and exclude, so its best to know how they work and how they an be political in and of themselves. I usually start with Civilization and the differing definitions of it; it doesn't take my students long to realize that as many definitions including writing as a necessary part of civilisation that suddenly a lot of people become 'uncivilized' or not a proper civilization- all by virtue of how we define terms we may even have taken for granted.

I'm not sure if this is appropriate for the sub, but could I ask for some clarification on the Mongol Empire being illiterate? As far as I understand, Genghis was the first to actually unite the Mongols and make it into a real empire, and one of the first things he did was institute a writing system. I guess it would be correct that the Mongol Empire started without a writing system, but they certainly acquired one very early on in the formation of their empire, which makes me wonder how that particular circumstance applies to this question.

A follow-up question: are there blanks on the map over extensive periods of time, from which we don't have sufficient knowledge, where this kind of lost culture could fit?

Or is there a compelling reason to be sure that pre-historic empires are simply not possible?

This is a much more answerable question: Is it possible to have large-scale political structures in the absence of writing?

Another question, but wouldn't large empires that want to be sustainable need to rely on writing to survive more than a few generations?