looking to fly into London on AA miles then another flight to Rome

AA certainly does fly from O'Hare to Rome. Not sure what you did wrong in checking, but I see lots and lots of flights. To answer your question, yes, it will be difficult to get public transport on Christmas in London, and a cab will be expensive.

AA does not fly into Rome in the winter season. Thanks for the reply.

Check with British Airways since you can use AA miles since they are a share partner with AA. Beware the high fuel surcharge with BA. You may need to check other airlines. We used our AA miles from London to Istanbul a couple months ago.

Another possibility - use Frequent Flier miles to London, then try an EasyJet or other airline to Rome. Wont be with your AAdvantage miles, though. Might still be cheaper than using your miles on BA, though.

LA - We frequently fly into London and catch cheap flights to other countries.... For London to Rome, we have used easyJet (Gatwick or other) and British Airways (Heathrow). I haven't been to London over Christmas, so I can't comment on transportation questions....

To echo what George said look into British Airways. When you fly from the US BA has a unique feature that let's you layover in London for any number of days before continuing on to your destination city or on the way back. This would allow you to simply book into Rome and choose to take a couple of days in London then continue on to Rome as a single flight. London is a BIG city and it's realistically about an hour from Heathrow into the city so if you take the time take enough to make it worth it. Never been there at Christmas - check out Rick's Christmas in Europe stuff for events. Heathrow is on the bus, train and tube - I doubt there's any day of the year that they have restricted travel that would really affect your schedule.