Oh -- I'm sorry. I believe it's "The Destruction of Sennacherib", by Lord Byron. Please permit me a tiny history lesson with fascinating modern overtones:

The Assyrians of today are descendants of the ancient Assyrian people who built the mighty empires of Assyria and Babylonia. Their capital, Nineveh (6000 BC--1500 AD or thereabouts), was near the modern northern Iraqi city of Mosul. Sennacherib was king of the Assyrians in about 700 BC. He conquered the cities of Judah and laid siege to Jerusalem; his records* say he won, and collected fabulous tribute, but the Hebrew Bible (2 Chronicles 32) says his soldiers "spoke of the God of Israel as though he were one of the gods of the other peoples of the earth, a work of human hands....because of this...the Lord sent an angel, who destroyed every valiant warrior, leader and commander in the camp of the Assyrian king," (185,000 men, reportedly), so that he had to return shamefaced to his own country. And when he entered the temple of his own god, two of his own sons struck him down there with the sword.   *(p://www.fordham.edu/halsall/ancient/701sennach.html).