Hekatombaion first appeared as two separate beings, one three-eyed and the other four-eyed.
In its first confrontation "3" was destroyed by Samidare, while "4" ran away from Yayoi.
In its second confrontation "3" (regenerated) was defeated by Yuuhi, only for "4" to arrive and eat the other to form its complete form.
It served as a passage way for Animus to appear, while the same called it "Gatekeeper".
The two Golems creating Hekatombaion
One half of Hekatombaion
Hekatombaion being used as a gate
One half of Hekatombaion
Three-eyed Hekatombaion (anime)
Four-eyed Hekatombaion (anime)