Things to see
Rome puts up a few big Christmas trees. Pinning these locations below:
St. Peter's puts up a big tree and nativity scene in their square. You can also go to Christmas Eve mass here.
This year the big tree that normally sits in Piazza Venezia will be in Piazza del Popolo due to construction.
Lights are strung down this whole Via, so it's worth going and walking down it. Especially at night.
Has a great Christmas market. It's not as full of vendors as it has been in the past, but you can still find some great treasures. They also had a merry-go-round last year. Plus this is a fun Piazza to walk around and you can stop for a treat or dinner too.
In the past, there has been a tree outside of the Coloseo, but they also have removed it
Other information
You'll sporadically see people roasting chestnuts on the street at little stands, and you can stop and buy them for a warm treat as you're walking.
Panettone is a traditional food eaten around Christmas time. It's like a sweet bread or fruitcake. You'll see it all over if you come for the holidays, and it's definitely worth trying!
It's important to book lodging and dining (especially for the nights of December 24th, December 25th, and December 31st) in advance. This time of year can be busy with visitors, so to ensure you are staying and eating at the places you want, book in advance!
On the above note - some museums and attractions might have different hours (particularly on the holiday days). Be sure to check the schedules and the hours before you leave so that you aren't surprised when you get here.
December 8th is when the Christmas festivities kick off, and this is traditionally when Italians decorate their Christmas trees. The 'Christmas Season' will then run through January 6th, which is the Befana holiday.
Depending on where you're from, Rome may feel cold (or warm!) to you. I am a native Minnesotan, so when I spent Christmas in Rome last year, it felt balmy. I definitely wasn't wearing t-shirts and shorts, but I wasn't as bundled as you'll see some people get. It was in the 50's (Fahrenheit) during the day, and typically sunny. At night it would get down into the 40's.
Regarding packing - during the day I felt great in jeans, sweater, and sometimes a light winter jacket (but again that might be my Minnesotan coming out). During the night, it did feel cold, and I appreciated having a coat and/or sweater. I'm also happy I packed slippers to walk around the house in, so my feet didn't get cold on the floors.
All the lights really do make Rome magical during the Christmas season. It's fun to wander through the center at night and see the lights, smaller trees, and other decorations that get put up (not to mention it's emptier at night).
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