Now, I don’t mean a culture that existed before writing, or one that was isolated from other literate cultures so that there was no one to keep the memory once the culture disappeared. Nope. This happened in the heart of the civilized world of antiquity, near the homelands of more famous groups like the Hittites and the Assyrians.
This culture’s name was Urartu.
We don’t know all that much about them, but they lived in the Iron Age, from the mid-800s BC to about 600BC. They had their own pantheon of deities, their own writing system, and a unified monarchy. Their territory included parts of what are today Turkey, Armenia, Georgia, Azerbaijan, Iran, and Iraq. For a while, they were one of the main military rivals of the Assyrians.
We don’t know exactly how Urartu fell, though we know they suffered raids and military defeats toward the end. What’s unusual is that within a few hundred years of Urartu’s demise, the people of the region had more-or-less forgotten that it had ever existed. Sure, the ruins of Urartu’s cities and fortresses were still there, but they were believed to be Assyrian ruins. There were inscriptions, but no one could read them. The people and culture of Urartu almost certainly contributed to the formation of the Armenian people, but to what extent is not known. The history of Urartu was not transmitted into the legends and histories of the Armenian people, at least in any easily recognizable way. While Urartu is mentioned in some contemporary sources (it’s the kingdom of Ararat in the Bible, for example), those references meant nothing to later readers.
The area formerly covered by Urartu was not exactly a stable region in the subsequent centuries. It was a border region between rival civilizations like the Persians, the Greeks, and the Romans, with waves of invaders from the Central Asian steppes periodically sweeping through on their way southward. This fact almost certainly contributed to the loss of historical memory.
It wasn’t until the 1800s when archaeologists rediscovered the existence of Urartu. Even then, studying them was difficult, as the main archeological sites were in dangerously lawless areas – two of the early expeditions were wiped out by local Kurds.
One other interesting fact: a lot of what we do know about Urartu comes not from their own records (mostly inscriptions on monuments) but from the records of their enemies, the Assyrians. The Assyrian royal archives, unearthed in the 1800s, included years’ worth of reports from Assyrian spies sent to report on Urartu.
So there’s an ancient civilization for which most of our historical knowledge comes from intelligence reports.