The pair, aged 24 and 25, were spied hanging out in the second tier of the ancient gladiator stadium at about 5.30am in Rome, Italy (04:30 GMT) on Monday.
Now they have been slapped with a 800 euro bill (£670) for illegally entering the site after a passerby alerted the police to the incident.
The American holidaymakers, who have not been named by police, told officers they were “just having a beer” - according to Italian reports.
The intruders had scaled the high railings to get in and climbed the steps to get to the second level of the monument where they were later spotted by a passerby.
A spokesperson for Rome’s carabinieri police force told CNN: “During the early hours of Monday morning some people noticed two young men drinking beer in the Colosseum, facing outwards on the second level.
“They alerted a police car nearby, which then stopped the two young men on Via dei Fori Imperiali.”
The 2000-year-old Colosseum closes to the public at 4.30pm.
Steeped in history, gladiators once fought among each other and wild beasts at the Roman amphitheatre.
In 2019, around 7.6 million people visited the Colosseum pre-pandemic.
