We don't know the exact date on which Hypatia of Alexandria was killed, but it was almost certainly during the year 415. She is generally considered the last major intellectual of the Classical civilization, and some historians use the date of her death to mark the transition from the Classical era to the Dark Ages.
Her life embodied the conflicts raging in the age of decline in which she lived. Several decades after Christianity was made the official religion of the Roman Empire and non-Christians were subject to increasingly vicious persecution, she remained obstinately pagan. At a time when dogma and superstition were crushing science and reason, she kept working to advance Greek astronomy and mathematics, even working as a teacher to pass on the treasures of the ancients. Orestes, the Roman governor of Egypt at the time of her death, had been a student of hers and still sought her advice at times -- a fact which made them both targets of the new religion which taught that a woman should be silent and never occupy a position of authority with respect to a man.
Hypatia lived through the siege and looting of the Serapeum temple (pictured above) by a Christian mob egged on by Bishop Theophilus in 391, an act which may have encompassed the destruction of the last remnants of the Library of Alexandria, though historians are unsure whether any of the Library had actually survived to that date. In 415 another Christian mob attacked her in the street, dragged her into a church, and hacked her to death with either shells or roof tiles. She was probably about 65.
Hypatia's life and death were dramatized in a 2009 film starring Rachel Weisz which I strongly recommend; it captures the feel of civilization collapsing into barbarism very well, as well as Hypatia's struggle to preserve the life of the mind in an age of gathering darkness.
About 400 years after Hypatia's death, much of the surviving corpus of Greek writings was rediscovered in the Middle East and translated into Arabic, leading to a huge revival of science and philosophy under the Abbasid dynasty of Baghdad. The thinkers of this so-called "Islamic" (actually neo-Hellenistic) civilization achieved great things, but faced a constant struggle against religious dogma and hostility to the life of the mind, though this time that hostility took a Muslim rather than Christian form. As of the twelfth century, the religious purists won out and the Middle East, growing steadily more hostile to science and philosophy, sank into stagnation.
The next revival, again driven largely by Classical inspiration, took place four hundred years after that -- the Renaissance, beginning in Italy and then spreading to the rest of western Europe. Figures such as Copernicus, Galileo, and later Darwin faced unrelenting hostility and obstruction from the forces of religious fanaticism and intolerance, but they and countless others fought doggedly on, and carried human knowledge and achievement to heights never before reached.
I think we've finally got the bastards beaten. Yes, the fanatical and the ignorant and the merely unimaginative continue to rail against stem-cell research, life extension, evolution, and on and on, and they've made frightening inroads into one major political party in the most powerful of our countries -- but their hopes of repeating what they did in the fifth-century Roman Empire or the twelfth-century Middle East seem vanishingly remote. We've come too far now, and our civilization is too widespread. Any one country that does sink back into ignorance and superstition will merely fall behind and become irrelevant, while progress continues elsewhere.
Hypatia, it took sixteen centuries, but you won in the end.