1 . One explanation for this strong statistical pattern is that traveling requires time and energy, and people have limited resources for it. At the core is the effort that people are willing to invest collectively to travel to certain locations, trying to optimize their days.

2 . People have been pouring into stadiums since the days of ancient Greece. In around 80 A. D., the Romans built the Colosseum, which remains the world’s best known stadium and continues to inform contemporary design. Rome’s Colosseum was 157 feet tall and had 80 entrances, seating 50,000 people. However, that was small fry compared with the city’s Circus Maximus, which accommodated around 250,000 people.

How many people could the Circus Maximus hold?