Which city does Isaiah 21:9 announce: "Fallen, fallen is ___!"?

Answer: Babylon

"Fallen, fallen is Babylon! All the images of her gods lie shattered on the ground!"

“Look, here come the riders, horsemen in pairs.” And one answered, saying: “Fallen, fallen is Babylon! All the images of her gods lie shattered on the ground!””— Isaiah 21:9 (BSB)