unroofed

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

那就是罗马椭型天竞技了，基本是综合功能体育。

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

天馆到封闭建筑转变，就可能是追求门票收入开始。