Here's a theory. I feel like the civilization that the Hae tribe is connected to could be similar to Rome and Greece, or was based off of these civilizations.
1. For example, Greece had a bronze period and the Hae tribe is the only ones in Arthdal with bronze weaponry knowledge.
2. Taelha dresses quite differently from the rest of Arthdal. Her dresses are very similar to Greek and Roman fashion.
3. The Hae Tribe fortress of fire- everything from the banners and candles to the wall statues reminded me of a medieval castle, or perhaps a Roman one.
4. Mihol referred to "Remus"- well in history, Remus was one of the mythological founders of Rome alongside his twin brother Romulus.
lololol ofc, with Arthdal being a mythical civilization, the Hae tribe origins could be entirely different.
Nunbyeol x Yiseuroobeu <3