unroofed

That must be the oval unroofed amphitheater in Rome. It was basically a stadium with comprehensive functions.

那就是罗马椭型露天竞技场了，基本上是综合功能体育场。

The change from the unroofed stadiums to sealed off buildings maybe the beginning that tickets were sought.

从露天场馆到封闭转变，就可能是追求门票收入开始。