The historical city centers of many Italian cities have in place a ZTL – Zona a Traffico Limitato – Limited Traffic Zones. This means that circling the restricted area is a ring of traffic cameras ready to take a photo of your license plate, and if your car is not registered as resident for the city center you will be getting a traffic fine sent to your home address through the post from the Italian traffic authorities. So of course this takes months to arrive and you are fined for each infraction – meaning that you can pick up many many fines.
So when you are planning your trip you need to bear this in mind. The most useful contact who can tell you about the ZTL’s will be your hotel. If your hotel is inside a ZTL you can give them your license plates for your rental car and you won’t get fined for every time you go into the ZTL (i.e. back to your hotel).
Obviously you need to request this BEFORE you start driving in the ZTL and the fines start coming in...
For more information see: http://ukinitaly.fco.gov.uk/en/help-for-british-nationals/living-in-italy/driving-in-italy