mitsho
Deity
That would make this 'Arch of Triumph' probably a left-over Roman Emblematic of some kind, since I don't know of any such structure associated with any pastoral group.
Well, if we are already at Age of Empires 2, a Triumphal Arch overflowing with treasures was the Hunnic Wonder, so maybe that's also an inspiration for why to include that Arch on the Screenshot.
The only pastoral arch structure I know is the Dothraki Horse Gate but we're then maybe not as historical anymore.