The Thing about Rome for me is that you can end up looking at a piece of historical beauty at any random corner of the city - be it from the ancient Rome, medieval times or renessaince. So it really is a city filled with layers upon layers of history unlike any other place - the Colosseum, Pantheon, Trevi, St Peters are just the tip of the iceberg.
And that kind of omnipresence of 3000 years of human history is quite chilling. The monuments seem to speak: about the continuous will and success of the powerful to leave their dent in the universe, about the kind of power & wealth it must have taken during its time and about the inevitable eradication of even the tallest monuments. They seem to be challenging the spectator: what will YOUR dent in the universe be!? Or maybe it’s just my upcoming mid-life crisis talking to me, not the history ;)