A mutated version of thaumaturgy to be exact. As above, so below. If you do something on a small scale and feed enough energy into it it'll happen on a large scale. I built a model city of Chicago in my basement once and basically did the same thing, except I didn't make a magic circle to contain people inside it. But, I think, that with enough power someone or something(s) could be doing that to us. The question is how they got us here in the first place. Also if there is someone or something, or the universe just fucked up and we're all about to die in the most boring city. Ever.
Another option is it's a basic magic circle, which are meant to keep things in. Or out. But there are mortals here who can't get passed it and that breaks every law of magic that I know and understand.
The real idea then is that with enough people we could theoretically combine our strengths and funnel energy into the damned circle and break it ourselves. Alone, I can't do it, alone you can't do it. And well, no one else that's maybe tried has had any luck either. Or else we wouldn't be here still.