Grazie Mr Epler!
Mr. Kern came through and provided excellent insight to my question about whether or not Christians were killed in the Colosseum in the first century. As any good expert does, she consulted other good experts, in this case Mr. Epler! Mr. Epler (our Latin teacher) knows all things Roman and offered excellent insight. The short answer is that my tour guide was right - there is no real evidence that Christians were killed in the Colosseum in the way that we might imagine. It's an interesting topic if you ever feel like digging into it, see Mr. Epler!