Tengri

This Holy Site is identical to a Native Trade Site. Allying with Natives allows a player to train special Native units, usually warriors, and also grants access to a group of improvements to that tribe. Native units do not cost any population spaces, but can only be built in limited numbers. Tengrism is an ancient animistic religion that was widespread in North and Central Asia. The sky god “tengri” is its main deity and was worshiped next to many natural spirits and souls. In Tengrism and related beliefs high elevations like mountain peaks are considered sacred places due to their proximity to the sky. The "ovoo" is a man-made stone heap that represents a peak and therefore acts as a shrine. The political legitimacy of rulers in Turko-Mongol societies and states was connected to Tengri and comparable to the Chinese “mandate of heaven” or European “divine right of kings”. The royal Mongol chronicle from the 13th century CE claims for instance that the ancestors of Genghis Khan are descendants of Tengri.

From the game's History encyclopedia, AoE3: DE 100.19.18309.