unroofed

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

那就是罗马的椭型天竞技场了，基本上是综合功能的体育场。

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

从天场馆到封闭的建筑的转变，就可能是追求门票收入的开始。