Last week I found myself with 24hours in Rome, and booked a last minute tour of the Forum and Coliseum with Through Eternity Tours. Like other who have posted on this forum, I could not possibly have had a better experience. Their website is a breeze, our group was small enough to navigate the sites quickly, and our tour guide (Federica) was impossibly nice, knowledgeable, and well spoken. It was a combination lesson in civics, art and military history, and architecture that will be hard to top. I couldn't recommend this company more strongly.