Maxentius went missing during the Battle of the Milvian Bridge, and his body was retrieved from the Tiber the next day.
Maxentius and Constantine had briefly ruled jointly, as attested by this ram's head fibula which can be dated to this period in AD 306-7. It was stolen from Turin, and more details about it are available at LootBusters here.
Sarah Bond: The Whole World in His Hands: Maxentius, Roman Scepters, and Power Symbols
The catalogue of the exhibition in Rome is not currently available outside Italy, but presumably can be found in libraries: I Segni del Potere. Realtà e Immaginario della Sovranità nella Roma Imperiale.
Sapienza has made a very interesting booklet available as a PDF here.
If you enjoyed this video by Adrian Murdoch, check out his book on The Emperors of Rome; Kindle UK, Kindle US, etc