Despite the fact that the Colosseum is one of the most important sites in Rome, there is no particular dress code to visit this massive building. Keep in mind that what to wear depends only on weather conditions and be prepared for the rainy weather. It depends on the season when you want to visit the Eternal City.
When in Rome, think about comfortable shoes because it is better to explore the city by foot
Moreover, pay attention to your bags since there are always many people near popular attractions of Rome, so don’t let your personal things to be stolen. The same with documents, it is always better to have an ID card with you. In addition, keep some cash with you since not all Roman points of interest accept credit cards when you pay for the ticket or just in case if you want to buy something like water or gelato while exploring the city.