Ironically, if you want to play the stickler, it’s “stadiums” in this context, not “stadia”. “Stadium” has two meanings, which many people seem to forget, and the pluralization is different for each:

1) A Latin word carried into English that refers to the measure of length used in Greek and Roman games for the size of their fields (roughly 180m). Proper pluralization: stadia.

2) A more modern English word referring to a tiered sporting arena surrounding fields that were measured to the aforementioned length. Proper pluralization: stadiums.

You can find more info elsewhere on the web with a simple Google search, I’m sure. Understandably, this pluralization is a source of confusion for many people, especially so since it does seem that it should be a Latin-style pluralization. Unfortunately, it’s not that simple.