Shower thought - I heard you had three, but what about four?

I don't wish to ruffle any feathers. My goal with this thought is not necessarily have a relationship like this, but rather just curious.

Over the last few days, I have been having this thought, about a relationship structure.

Four people under one roof, all connected with one another. I read about people wanting a triad, and even having them. But what about a four, five, or more people having a romantic connection? Has anyone been a part of such a thing, or heard of such a configuration?

Bonus points; if there is some story (book, show, or film) out there that features this idea.

Maybe they are common things and I have just missed it. Maybe they are super rare, and this is just intrusive thought. Either way I need more poly friends, to talk out these ideas with.