Lost knowledge - The Great Library of Alexandria
The Royal Library of Alexandria was once the largest in the world. It is assumed to have been founded at the beginning of the 3rd century BC during the reign of Ptolemy II of Egypt and is estimated to have stored at its peak 400,000 to 700,000 parchment scrolls. Not surprisingly, the Great Library became a symbol for knowledge itself.
All that is left of many of the volumes are tantalizing titles that hint at all the history lost from the building's destruction. Few events in ancient history are as controversial as the destruction of the Library, as the historical record is both contradictory and incomplete. There is a growing consensus among historians that the Library of Alexandria likely suffered from several destructive events, notably burnings by the Romans, but that the destruction of Alexandria's pagan temples by Christians in the late 4th century was probably the most severe and final one.
Burning of the Library of Carthage - the Romans
Burning of the Great Library of Alexandria - Romans & Christians
Burning of the Sibylline books - a combo this time of Christian (Arian) Roman General
Burning of loads of South-American culture by the Conquistadores
Thousands of Sanskrit works which disappeared in India in the reign of Emperor Akbar
It was the year 146 B.C. Phoenician Carthage was in its death throes at the end of the third, and last, Punic War with Rome. The Romans had devastated the city, and only the citadel with its temple remained to be conquered. Finally, the courage of the commanding general of Carthage faltered. He crossed the lines, fell on his knees before the Roman general, and begged vainly for his life. Just then, above them on the wall, surrounded by fires from the burning temple, appeared the wife of the Carthaginian general, their two small children in her arms. She screamed curses on her husband for his cowardice and curses on the Romans for their destruction of her city. Then, pressing her children to herself, she jumped into the fires, choosing death for them all rather than lives of slavery.
Needless to say, she won the respect of the Romans and of all those who have heard her story since. It is said that the conquering Roman general wept as Carthage burned. Laid out before him, he perceived the transience of all human constructs, and foresaw the day when his own city, Rome, would suffer a similar fate.