[Doctor Stochastic]

It was actually the Circus Maximus (next door to the Coliseum.) The Coliseum itself was sacred and didn't allow for executions. (It did allow for combat.) Hollywood (and movies like "The Robe" and "Quo Vadis") likes to use the Coliseum because it looks neat.

Of course, the legend of Androcles is from Aesop and thus predates Christianity by some time. G.B. Shaw had a version, too. (He also re-wrote Pygmalion.)

[AndrewC]

It was actually the Circus Maximus (next door to the Coliseum.)

I don't know, wasn't there, but the Catholic encyclopedia, says it is likely some Christians were martyred there. Who knows exactly where, but no doubt they were martyred.