Architects built the Colosseum to be the largest arena in the world. They built it to hold between 50,000-80,000 people.
The roman architects devised an ingenious system of entrance,corridors,and staircase that allowed the crowds to enter and exit the Colosseum quickly and easily.
By using so many seperate entrances the architects solved the problem of crowd control- the Colosseum could be cleared in less than 10 minutes.
Citizens could get into the Colosseum for no expense.