Emperor Caligula (12-41), among the most infamous of Roman emperors, is showing a secret soft side by tending the “giant chameleons” in his personal menagerie. The one he’s feeding is showing its gratitude with a vibrant color change in its plates.
I actually don’t know for sure if any Roman emperors ever kept menageries or zoos, but the Egyptians and Mesopotamians had them thousands of years earlier, so I think it likely the Romans did too. Certainly they were big on displaying exotic wildlife at public arenas (before having them disembowel troublemakers or fight gladiators, of course). As for how Caligula would have access to these particular “chameleons”, I’ll just say his legions found an anomalous “glitch” in the fabric of the Universe that allowed unparalleled travel throughout space-time.