The Ancient City contains the remains of a temporary settlement used by Queen Elizant I and her people before founding the Ant Kingdom. It was eventually abandoned as they searched for a location to create a permanent settlement.
Immediately outside the city are a number of tanks adorned with the crest of the Ant Kingdom. They were used by the Ant Queen during her search. Due to their damaged state, they had to be left behind.
Initially, when Team Snakemouth first arrives, the city is inhabited by hooded and masked bugs that speak an undecipherable language. After defeating the False Monarch, the other inhabitants flee, leaving their masks behind. The False Monarch's nature implies that these citizens were also Mothflies in disguise.
A Venus' Bud can be found inside a dilapidated building with an inn sign at its front.
Kabbu: This place has seen much better days. Vi: Why'd all these bugs wanna live here? Leif: Their choice of home is not the only strange thing about them... Kabbu: They do give off a peculiar feeling... Let's be on guard.
Outside (After False Monarch)
Leif: Everyone's gone... Vi: Was everyone a bunch of Mothflies in hoods too? Kabbu: A mystery... Just what in blazes was going on here...?
Tent (Before False Monarch)
Kabbu: ...! T-Team, I feel a great threat. Be on guard!
False Monarch Room (After False Monarch)
Vi: What was UP with that thing!? Kabbu: I struggle to comprehend how a mass of flies could behave that way... Leif: This tent was here before them, right? We wonder if... Elizant stayed here at some point. Vi: This ain't fancy enough for a queen, right? Leif: If they were traveling, there'd be no place for too much luxury. Kabbu: Sadly, there's no real way to be sure. But it's fun to speculate. Leif: Yeah.
Venus' Bud (Before False Monarch)
Venus: This settlement was used by the very first Ant Queen when she first arrived in these lands. ...But now it's full of these weird mask-wearing bugs. What's their deal?
Venus' Bud (After False Monarch)
Venus: Huh, the weird bugs all left. I supposed you had something to do with that, right?