Bluebulb Projects' The Measure of Things presents:
31,000 is about three-fifths the number of Seats in The Colosseum.
In other words, the count of Seats in The Colosseum is 2 times that amount.
(a.k.a. The Coliseum, a.k.a. Flavian Amphitheatre, a.k.a. Amphitheatrum Flavium, a.k.a. Anfiteatro Flavio or Colosseo) (Rome) (estimated)
Built between 70 and 80 AD, The Colosseum was a central attraction of Rome, capable of seating 50,000 spectators for various events including plays, war reenactments, and gladiatorial matches. The structure was estimated to require 100,000 cu. m of stone to construct. It remains the largest amphitheater in the world.