past or passed?

Please help choose: past or passed.
The newly-crowned first king of Italy announced, "The time of the Roman Empire is _____."

(Please pretend the king spoke English.) I’m writing a transcript of a spoken recording (not about Rome), and I don’t know which word was said, but I must use one of the two. The speaker definitely said is, not has. Other questions I’ve found here about past and passed don’t quite have this context.