No one really knows for sure what it was going to be for, but we do know that it was never implemented. Please, get around to implementing whatever it was you were going to put there; we at least deserve to know what it was supposed to be.

For those not in the know, I'm not talking about The Pit. The Colossem has two maps- One of them is The Pit, for Pankration. The other was a much smaller map, and has another entrance in Whitegate; but its true purpose was never established and it was never released. There's still an NPC there with a locked door behind him.

I'm pretty sure the consensus among the community was that it was going to be some sort of arena for people to have duels or something, but it was never officially established, as far as I know.