Psalms 9:6 The enemy has come to permanent ruin. You have uprooted the cities, and even the memory of them has perished.
It was comforting for the psalmist to keep in mind past enemies who had been troubling to his nation but who now exist no more. It gave him perspective on the trouble he now faced from present enemies. Hitler, Stalin, Caesar, etc. — all gone from the scene. While these examples are still remembered, countless others do not even come to mind. God is the living God. His enemies are all temporary.