Diamonds can sometimes be found in them

STADIA

Think of large venues where sports are played—the plural form of the word might remind you of ancient Greek or Roman gathering places.

The clue plays on two meanings of "diamonds." In baseball, the infield is called a diamond, and stadiums (or "stadia," the plural form) are where you’d find them. The word "sometimes" hints that not all stadiums are for baseball, but the connection is strong enough to lead to the answer. It’s a clever way to turn a sports term into a crossword solution.