What does upgrading Amphitheatre do? (and what caused it?)

I have an upgrade ^ symbol on Aqueduct and Amphitheatre. I know the Aqueduct upgrade will give me Hydro Plant and came from Robotics, but what about the Amphitheater? It's not mentioned in the wiki.


Solution 1:

Just tried it: it turns into a Broadcast Tower that works like Amphitheatre but more effective. This reddit thread has some info.

The popup window says Culture 5/sec, Unhappiness reduction -75%, Max Culture 525.

As opposed to Amphitheatre 0.005/tick (=?), Unhappiness reduction -4.8%, Maximum Culture +50