tl;dr: how do you know if one of the AI competitors has already built a Wonder?

Longtime lurker. Picked up this game a month ago and just went mad trying to find an answer to this very basic question. I already Googled and checked Reddit, but I cannot find a list of previously built Wonders.

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Shortly after learning Economics, Big Ben was not on the list of buildable Wonders. Absent. not even grayed out with “no suitable location for this Wonder” in red. My strategy was: be frugal and double up to “buy” a win.

It had to be already built, but I was on a huge map with lots of AI player territory I never explored; panning across the map wouldn’t work. So I looked for the Completed Wonders list. Found none. Is there no Completed Wonders list!?! I Googled and Reddit said the icon would be gone from the Econ Tech tree if the Wonder was already built. Big Ben was there, though, as if to taunt me with a hidden mechanic.

So I went through the Gossip, filtered by City, and ONE HUNDRED TURNS PREVIOUSLY Pericles had broken ground for it in Sparta, of all places. We were allied so then I could just look and confirm it was already built.

My question is this, how do you know if one of the AI competitors has already built a Wonder? In the words of so many inventors, “There has to be a better way!”