back packs

Do you mean the Cività day bag? If not packed to the gills it should be OK most places. A messenger bag is a better bet, though, as it is treated more like a woman's purse. Be aware that the Galleria Borghese allows NO bags at all.

At the Borghese gallery is there a place to store a bag?

Yes, Galleria Borghese DOES have a bag storage. Free as I remember.

Often if a bag has backstraps it is considered a backpack, even if you can carry it over one shoulder.

Restrictions can vary by museum/attraction.
These are the bag restrictions for the Vatican Museums:

"It is obligatory to deposit in the cloakroom suitcases, backpacks and containers with dimensions larger than cm 40 x 35 x 15. It is obligatory to deposit in the cloakroom bags and bagpacks which are cumbersome, except those small-sized, that carried on shoulder, don't jut out by 15 cm from the body's shape in its highest point."

These are the restrictions for the Palatine and Forum:
"It is confirmed the prohibition of bringing backpacks , camping , bulky bags and luggage"
Yes, it's vague so err on the smaller side. There is NO place to check bags at either place.

For Pompeii and other noted sites:
"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. Visitors can leave their bags and personal belongings at the free locker room at the access gates."

And as mentioned, the Borghese doesn't allow any bags at all. Your RS bag should be fine for practically all churches and many museums and other venues but it's best to check their individual websites in advance.

I didn't have a single problem in Italy carrying my backpack into any event. It's a normal sized school backpack I've had for 10 years. I didn't go to every museum in the country, so it's possible some places will have restrictions, but I went to most of the major places in Rome and Florence.

Yesterday at the Colosseum, there were plenty of backpacks. You were asked to open the packs for a quick look and then they scanned it with a hand held scanner and let you right in.

The Borghese gallery requires you to check all but the smallest bags. They have a free storage area for this.

The Vatican museums will allow most bags inside but the really large backpacks must be checked.

Most other sites have restrictions, such as the colosseum/forum/palatine hill but a lot of time those restrictions aren't enforced. It's better not to have a backpack that's too large or you run the risk of being denied entry. All bags will go through security checks before entry.

Donna