Similarly, my take on antiquity was that it was basically in social decay from about 200 BC on. The Hellenistic period marked a long swing toward stagnation, the slave based economy was holding technological advancement back, there were fundamental problems with the Greek moral/ethical system (something Socretes was already getting into hundreds of years earlier), people were already looking backward rather than looking forward, and the Hellenized culture was falling into decadence and apathy. I mark the beginning of the end to Cassius's sacking of Rhodes (42 BC), and the loss of the Library in Alexandria (at least in part, date uncertain, but possibly 48 BC). They weren't lethal blows to the learning of the Ancient world, but after that technology is every bit as stagnant as it was in the Dark Ages. The writing goes on for several more centuries, and Roman survives through a couple of purges, but the energy is already going out of the ancient world long before anyone recognized the lights were off.