Throughout history invaders have tried to wipe out everything that defined the conquered culture and this included destroying books. I have a list of nearly 200 book burning incidents throughout history.
The earliest was the destruction of the city of Ebla near Aleppo in Syria. In 2300 BCE the city was razed to the ground by Akkadian invaders burning thousands of texts in the Kingdom’s library. Some clay tablets survived the fire by being baked. These bore an ancient cuneiform text (see the talk Where Books came From) . In 612 BCE the Assyrian capital Nineveh was destroyed by a coalition of Babylonians, Scythians and Medes. The fire destroyed the library of Ashurbanipal where King Ashurbanipal had amassed texts and tablets from various countries. There were leather scrolls, wax tablets and papyrus all destroyed but again the clay tablets survived to be discovered in the 19th Century