Don't take to much baggage!

12/12-12/15 Rome - you can take the train to Termini. Taxi lines are very long at Termini/
Bus to Siena evening 12/15 - to get to the hotel can be a problem. Many streets in the city center are only for pedestrians.
12/16 Siena
12/16 evening bus or train to Florence - You arrive by train in the city center. In front of the station are buses from Hilton and others. Also other buses.
12/16-12/21 Florence
Train to Venice evening 12/21 With the train you can direct walk to one of the public boats.
12/22-12/23 Venice
12/24 depart Venice early am. There are private boats to the airport, don't know about another connection.

Have fun.

I have hotels reserved for all nights of the trip, but they are all changeable and refundable reservations.

We do not plan to rent a car; we plan to travel inter-city by train and bus[/QUOTE]