Posting this heads-up due to the number of questions asked about it lately.
If you are using RS guidebooks instructing you to use the Coopculture website to buy your Colosseum tickets, that vendor changed earlier in 2024 so too recently to have been corrected in the books. The NEW official ticketing site is:
https://ticketing.colosseo.it/en/
Tickets sell out quickly when they become available - usually about 30 days in advance - so jump when tix for your dates come up for sale!
This is a prime example why certain information in even the best, most current guidebooks can be outdated before they've gone to print. Details such as hours, entry fees, closures and, yes, ticketing vendors can change shortly before or after press dates. Use your books for the background/history of the attractions you wish to visit but use their official websites for the most current visiting details. Don't know what those websites are? That's why there's a forum! :O)