Why the Colosseum Still Stands

Nearly 2,000 years old, the Colosseum remains the largest amphitheatre ever built, seating 50,000 to 80,000 spectators behind 80 numbered entrances. Roman engineers used volcanic ash in concrete that slowly self heals cracks, a chemistry modern science only recently explained. An awning system called the velarium shaded the crowd, rigged by sailors from the imperial fleet.

The inaugural games in 80 AD ran 100 days. Earthquakes and stone robbers took their toll, yet the skeleton still defines the skyline of Rome..