Backpacks welcome or leave in hotel?

If a tourist sight doesn't allow back packs, they'll often have a coat room where they can be checked in and out. The Vatican Museum is one of those places. Go ahead and take your backpocket and check'em in the coat room.

It's hard to carry a good corkscrew in your back pocket.

Note also that some places that allow backpacks DO require that you carry them by hand rather than on your back so that you do not inadvertently harm exhibits or architecture.

Pompeii has specific sizes of bags that they won't let inside so if your backpack is large you may need to check it. The colosseum has a ban on them as well but does not have any storage for them. If by crypts you mean the scavi tour under the basilica you won't be allowed to take anything larger than a small woman's purse with you. They are very strict about that. The Vatican museums has a size limit as well on what they'll let inside. They do have a storage check area.

Donna

Be a little careful about checking a bag at the Vatican Museum. If you have checked a bag, you must walk all the way back through the museum to the entry in order to get it. If you are with a tour group, or can slide through with the tour groups, you can go directly from the Vatican Museum/Sistine Chapel into St. Peter's, which can save A LOT of walking and time.

The Coopculture site appears to have removed the text regarding a backpack ban at the Colosseum BUT it's still in place for the Forum and Palatine. if you're doing all three sites, you'll want a smaller versus larger bag:

http://www.coopculture.it/en/heritage.cfm?id=4

"It is confirmed the prohibition of bringing backpacks , camping , bulky bags and luggage / trolley, can be introduced medium and small size backpacks to shoulder, which must be checked, as any other bag, with metal detectors, opened and visually inspected by the Urbe Security Institute, responsible for the entrance inspection."

In any case, as reasonably small as possible is always advised so as not to bump other tourists or walls/displays.

The guidelines for backpack/bag size at Pompeii are here:

http://www.coopculture.it/en/heritage.cfm?id=1

"STRICTLY FORBIDDEN to introduce inside the excavations of Pompeii, Herculaneum, Oplontis, Stabia and the Museum of Boscoreale, handbags, backpacks, luggage, cases, larger than 30x30x15 cm."

I agree with the comment above about the bag check in the Vatican. We were just there and the line at the bag check was very long. Also, you definitely want to try and use the "back" entrance between the museum and the basilica if possible and it is on the opposite end of the museum. My family of four had two very small back packs - each carried two water bottles, a small sweater (to cover shoulders) and a very small messenger style camera bag. No one said anything to us about these bags because they are small and fit close to the body.
It was the same at the Coliseum - those with larger packs were directed to the longish bag check. This elf us with small bags were waved through.
If possible, split your walking around essentials into two small bags rather than one larger one.