Mystery Circle

The school-turned-condo building we're working in has 3 floors; we're currently working on the 2nd. Today I noticed something strange in one of the former classrooms on the 2nd floor.

In the center of what was once a classroom, there are a series of holes cut into the floor, and the holes form a perfect circle, maybe 10'-12' in diameter. The holes have since been filled in with wood plugs, and nobody seems to know what the purpose of the giant circle and holes in the floor were.

Until somebody can figure this out...not knowing what those things were for is going to bother me a little bit.