The Eurostar trains going to Rome from Florence and Arezzo are frequent and give you a great time schedule. Leaving Florence at 6,40 in the morning (and subsequently Arezzo at 7,14 in the morning) you can be in Rome by 8,30 and literally have the enitre day in front of you! There are several options for going home and the second last Eurostar is at 9,30 in the evening - so you can literally have the whole day in Rome. And with a place as huge as Rome even one day isn`t enough, the Romans will tell you not even a life time begins to scratch the surface of all there is to see in this incredible city.
Check the train schedule before coming in, the Italian train system does offer different hours during the course of the year (www.ferroviedellostato.it). There are ealier and later trains, but they take longer and are not all direct, the Eurostar means NO CHANGING TRAINS - you get on, read the paper, drink a cup of coffee and await the adventure. We would like to mention its airconditioned in first class, and well worth the few extra euros in the months of July and August.
Our most sincere suggestion about Rome is please be sure your personal belongings are secure - Rome is a busy city and stray hands are everywhere - especially in your pockets! There are so many great things to see in Rome, that you really need to decide what is a must see for you! The first place to walk over and see EARLY in the morning is the Coloseum. Get it early while it isn`t too hot, it is only a 10 to 15 minute walk from the train station or the metro will leave you off right in front of it.
If you decide that you want to see Capella Sistina then get over to St. Peters and put yourself in line ASAP, before it wraps itself around the vactican twice over. You will want a map of Rome, because it will literally help you get your feel about town. And I have been told that the metro in Rome is very efficient - personally the joy of walking the streets in Rome and every corner having some piece of history just sitting there to be discovered has lead me to walk the streets and catch buses more than taking the underground train system.
Anybody who ready "Angels and Demons" is not going to want to miss the Pantheon, it was under restoration in 2004 (and judging by Italian timing it will probably still be under restoration...) however it doesn't take away from the mystical perfection of this place.
The best thing about Rome is that it is walkable, and you never really have to feel like you missed out on something, becasue everywhere you go there is something to see. Prices are reasonable and the Romans are very friendly people. If you are there in the summer they are particularly famous for their cafe granite (iced coffee with whip cream on top).
Don`t forget to stop by the fountain of Trevi and through in your two cents (not much more because the locals stalk the fountain with a magnet to collect the larger coins.) The tradition has it that if you leave a little money behind you will be assured a return trip....
ROME IN THE EVENING:
It could be really worthy to take a couple of days more to stay at Rome for one or two nights, before or after your trip in Tuscany. Rome in the evening is really amazing! You can do this by car... park in the streets of the centre or "Lungotevere" (along the river) - just pay attention not ot enter the "ZTL" (Zona di Traffico Limitato - this road sign followed by a red circle means you can't enter by car in some zones of the historic center).