I would like to know how hot/cold/humid does it get in the excavations - we're scheduled for a late morning tour and I would like to get an idea about what to wear.
I know about the dress code - that's not a problem - but I'm not sure if i should bring something with long sleeves (a light sweater??)
We're going in about 10 days so I know it will be hot outside and so I don't want to carry extra stuff if not needed.

Thanks.

It will be hot and humid too. It seems more humid down there to me than outside even though there are supposed to be humidity controls (you go through some airlocks).

In July I took a light covering and removed it immediately.

Even in April I had to remove my very light jacket.

we were there in February when it was snowing outside so it seemed nicely warm to me.

We were there in September and it was pleasant. I do believe that much of Europe is having an abnormally cool summer.

Thanks everyone

We were there July 12 and it was hot and very humid. One elderly gentleman seemed to be having a rougher time with it than the rest of us. I asked him if he was OK. Dress cool, but being ready wardrobe-wise to go into the basilica afterward. I definitely recommend taking a bottle of water with you (backpacks are not allowed but you can take a small bag) just in case. It does get better the end of the tour when you go into the newer part.

Maybe it won't be so bad in the fall or winter if that's when you're going, but summer was tough when it was in the 90's outside.

OK, so we're back. The Scavi tour was definitely one of the highlights of our days in Rome - we were lucky to have a patient and informative guide who did not rush us through.

Now about the temperature inside - it was a bit better than I expected - warm and humid but not unbearable by any means.I didn't feel the need for water but my small, cheap, paper folding fan really got a workout ;-)

Just an FYI: The underground space is kept humid (controlled) to protect the structures and artifacts, so it will always be humid in there, no matter the season.