Hi Caroline..Some suggestions for your trip. There are some real good pickpockets in Europe. Although typically you will not see the violent crimes we may have in the US there are some great pickpockets in some of the big cities in Europe and Barcelona and Rome are good examples. You may want to consider putting your purse, etc. under your sweater of shirt. They are good at cutting straps so fanny packs or exposed straps are not the best secuirty. We have been to Barcelona a few times and in one case the lady was getting on the bus and they just walked, cut her purse strap and ran.
It is not something that should make anyone scared but rather just to take good precautions.
In Rome I think the On/Off bus is a good way to see the city. You can get off at interesting points and then get back on the next one.