The official tickets for the Colosseum are valid also for the Roman Forum and the Palatine Hill. On the Palatine Hill there are the ruins of the Emperial palaces whereas in the Roman Forum there are the ruins of the most important administrative, religious and financial buildings. 

The price is 18 euros for adults, 4 euros for students (with valid student card) with the age between 18 – 25 and free of charge for children under 18 years old. You should always bring your ID card or student card if you want the reduced price. 

At the moment (July 2022) tickets are only available online. Prebook your tickets if you want to avoid long lines especially on weekends and in high-season. Read here if you want to know when it is the best time to visit Rome

The special tickets for the Arena and the Undergrounds cost 24 euros. 
For the Arena and the Undergrounds the reduced ticket is 4 euros and the children under 18 are free of charge.

The best experience to discover the ancient Rome is to book a guide or a guided tour.