The world's oldest known library survived because its city was burned down

King Ashurbanipal of Assyria assembled thousands of clay cuneiform tablets in Nineveh in the 7th century BC, covering medicine, astronomy and myth. When the city was sacked in 612 BC, the fire that destroyed the palace baked the clay tablets hard instead of destroying them. Archaeologists rediscovered the library in the 1850s, giving us our earliest copies of the Epic of Gilgamesh.

— Austen Henry Layard and Hormuzd Rassam (excavators), Library of Ashurbanipal — Nineveh, rediscovered 1850s; British Museum collection