10 Hours layover in Rome airport. WHAT TO DO?

I have a 10 hour layover in Fiumicino Airport in Rome. I arrive at 12 PM and leave on another flight at 10 PM. Do I have enough time to visit the Colloseum? if not, what do you suggest I do during these hours? Details about the costs are appreciated. Thanks!
Update: THANK YOU ALL FOR THE WONDERFUL TIPS!
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