I just spent a week in Italy, and found that the tourist crowds are more annoying than I had anticipated. I found I was simply unable to enjoy myself due to the crowds, so I ended up skipping some of the common highlights, such as entering the Roman Colosseum, and many of the exhibits at the Vatican Museum.
If I want to return to Rome at a later date, when can I enjoy these sites, and specifically the Roman Colosseum, with the smallest crowds? What is low season? And if there is a difference, which is the lowest volume day of the week during this season? Weather, travel prices, hotel availability, etc, don't matter. I just want to enjoy the sites with few other people.
Also, if it matters, I'm only interested in entering the sites as a normal member of the public (special group reservations, exclusive invitations by the Pope, etc, are not of interest to me).