The culture of the ancient world was preserved during the Middle Ages at a fairly low rate. Some works survived unaltered, others survived in new, abridged and modified forms, while others simply didn’t make it at all. During the Renaissance, the West managed to salvage a great deal of ancient literature and cultural output from oblivion, but most of what could have been preserved, most of what we today could have easily conserved (had we had it), had been lost.
More ancient books were recovered between the years 1400 and 1500 than between the sixteenth century and today. At the beginning of the seventeeth century, Europe knew as much about the works of ancient Greece and Rome as we do nowadays, and exceedingly more than what Petrarch, for instance, standing at the extreme height of the medieval period, had inherited from almost a millenium of book production and transmission.
The Middle Ages recovered what they could from the fallen ancient world, given the priorities of its custodians of the written word. Human memory makes selections based on the individual’s past experience, desires and aspirations. A culture makes selections of what to keep and what to let go based on similar criteria. A lot of cultural capital was abandoned in the West after the 500s AD. The memory of ancient myths, ancient history, ancient thought, ancient lifestyle was forgotten in the West as the books which had preserved it were no longer there. A state of mild amnesia from which Europe would wake up one day, transformed and renewed.