Only one full day in Rome! What to do!

Since you have such limited time and have a specific interest you might consider a tour that covers it. For example this one https://jw-rometours.com/ or this one https://www.viator.com/tours/Rome/The-Christianity-in-ancient-Rome/d511-20217P5 I have no experience with any of them but you can check reviews and google more (I used bible tours rome to get these).

As above, a full day tour which covers most of what on your list is probably the best bet. I'll reference these tour companies which have gotten many positive reviews on the forums. I'll also suggest that you book directly with a tour company versus a 3rd-party like Viator (they don't operate tours; they're just a clearing house for companies that do. ) That way if something goes awry you're working with company responsible for conducting your tour versus a middle man.

https://www.walksofitaly.com/rome-tours/rome-in-a-day-tour/
https://theromanguy.com/tours/italy/rome/rome-in-a-day-tour
https://www.througheternity.com/en/rome-tours/rome-in-a-day-tour.html

There may be additional resources people have used. Mamertine isn't included in any of these; it's not considered an attraction most visitors want to see, and there's only so much that can be squeezed into an all-in-one-day tour. Just the Colosseum/Forum + the Vatican Museums will involve a lot of walking.

The Vatican Museums, where the Sistine Chapel is, are closed on Sundays.

If this is Tuesday, it must be Belgium--as the old movie title stated. 1 day in Roma is too little. My 1st visit was 3 days. Then my son & I were there 4 days & that was 3 & 4 too few.

We had a plan & while accomplishing that found ourselves in unexpected, delightful situations (Roma market for picnic ingredients that we ate while resting in an alley near the Pantheon & Contarelli Chapel, the bib needed for pasta at the local back street restaurant---best meal of the trip so ridiculously cheap, the World Cup viewed during eats & wine price negotiation at another back streets outdoor tavern within sight of the Circus Maximus) We took our time, searched, & discovered.

You will say you were in Roma--but 1 day will disappoint unless you concentrate on just a couple close sites

You can never see, even if you toured a 24 hour full day, the places you list. My suggestion: plan more days in Roma.

OR pick 1, 2, or 3 sites fairly close (like the Colosseum and the Forum). My son & I easily and leisurely enjoyed this sites. I just signed up for RS 7 days in Roma. My 3rd visit because there are more Caravaggios I must see. ab

Dear OP, you know your reasons for your schedule and I respect that this is the amount of time you have.

I would stop and think about what is the most important to you. Other people’s preferences really don’t matter here, only yours. I did like the idea of the day tours listed above for efficiency allowing to see several sights. Just make sure it includes the sight that is most important to you.

Since you are going during a very busy summer travel season, I'd check out those links from Kathy and pick an organized tour that is available on the one day you have. You will likely not be able to see all the things you want even on an organized tour. FWIW seeing the outside of the Colosseum is pretty cool even if you don't go in.

Also since you're going in August, I'd also suggest taking a tour that leaves as early as possible in the morning - it's likely to be very, very warm. Best of luck.

Hi, you've gotten some very good advice above, and I agree with the idea of choosing a day tour so you get to see as many of the sights as possible. IF you have the energy after that day tour, consider taking a passeggiatta, an Italian evening stroll, hopefully with a gelato picked up along the way, perhaps start at either the top of the Capitoline Museums looking out over the Forum, (it's past the statue down to the right) , or walk along the Forum down to the Colosseum with lights on it, (personally, it's just me but I've been inside and I prefer the outside lit up at night). Or just go sit in Piazza Navona and enjoy the people outdoors doing the same....

Another alternative to yet more walking after the day of touring, would be to look into the evening golf cart tours, haven't been but I see the sense of taking one to see some of the smaller, out of way places.

About the question anything historically connected with the Bible, this leaves me a bit perplexed. Unless you mean St Peter, in which case it would be Vatican City perhaps? If you mean paintings, in addition to the Vatican Museum there are many many churches to see with a silly amount of paintings. If you're thinking of ancient Christianity, agreed, best to take a specialized tour. One of the oldest churches in Rome built upon a very early Christian meeting place is the Basilica of Santa Maria in Trastevere, but there are so many! Ahhhh, just realized maybe you mean the ruins of early Christian life in Rome? Let us know where you're staying, maybe some other ideas will pop up. Don't forget to eat a meal! Consider booking dinner ahead near where you're staying. Have fun, Rome is an incredible city.

PS, Plan on HEAT, perhaps buy a sun parasol? Figure out what to wear (not shorts if you're going into churches or the Vatican museum), pick loose comfy clothing, wear GOOD walking shoes, plan breaks, how to stay hydrated, many museums won't allow backpacks... and stay in central Rome so it's easy to get around.