At the intersectionof all roads, in the rocky fortification, settled The Fourth tribe of all nations and founded a city called Arza.
It was a strictly established caste system: lower ranks of society lived under the Great Bridge and most of them were miners. Middle ranks consisted mostly of merchants, while the highest rank of society and the clergy lived high up in palaces and temples.
The highest priests lived in The White Temple, the uppermost place in the city, that drew energy from the huge Rock Crystal who stood on the Onyx and was surrounded with 4 Carnelians. These priests were visited by emperors from all around the world in order to interpret their dreams and predict their future.
As a naturally well-protected fortress, with one entrance to the city, it was a neutral and safe zone for the exchange of goods between tribes.
To this day, the Main gate remained firmly shut, and the whole city is deserted for thousands of years.
The White Temple is facing the Rosette Nebula next to the Orion's belt, because they believed to originate from the constellation Monoceros, and that one day their ancestors will come back for them and that they will return home.
Whatever they were waiting, something did come for them, because they disappeared without a trace.
*Submission for ArtStation Challenge Ancient Civilizations: Lost & Found
https://www.artstation.com/contests/ancient-civilizations/challenges/15/submissions/12928