The public transportation system in Rome is quite comprehensive and, if you plan your route in advance, can save you loads of time. Using a smartphone and downloading an app (Roma Bus, Moovit, Google Maps, etc.) is an easy way to plan your route. Keep in mind that there are multiple bus stops convenient for the Colosseum and, depending on which direction you are coming from, not all of them say “Colosseo:”
COLOSSEO MB* (Colosseum metro) : use bus #51; 87; 75; 117; 118
SAN GREGORIO OR CELIO VIBENNA (Palatine Entrance) : use bus #81 or 75
COLOSSEO (for Trams) : use tram #3 coming from Trastevere/Ostiense direction
COLOSSEO/SALVI N. (for Trams) : use tram #3 coming from Valle Giulia/San Giovanni direction
*ON SUNDAYS : the buses will use a deviated route and will not stop at the metro station bus stop. Instead they will stop behind the Colosseum and you can get off at either SAN GREGORIO or CELIO VIBENNA
