Here's what I mean:
The most important invention of the last two thousand years was hay. In the classical world of Greece and Rome and in all earlier times, there was no hay. Civilization could exist only in warm climates where horses could stay alive through the winter by grazing. Without grass in winter you could not have horses, and without horses you could not have urban civilization. Some time during the so-called dark ages, some unknown genius invented hay, forests were turned into meadows, hay was reaped and stored, and civilization moved north over the Alps. So hay gave birth to Vienna and Paris and London and Berlin, and later to Moscow and New York.
- Freeman Dyson (Professor of Physics, Institute for Advanced Study; Author, Many Colored Glass; The Scientist as Rebel)
http://www.edge.org/responses/what-is-the-most-important-invention-in-the-past-two-thousand-years
But the Romans also conquered as north as modern England and France where the winters are currently harsh. Wouldn't it be reasonable to expect them to have cold winters back then too, and so to need hay?
You are completely right to call complete and utter BS on the part of this "professor". That guy really needs to stick to his own field of physics rather than pull random and completely speculative answers based upon his own guesses.
Here's a random citation to back you up:
"Evidence for animal stalling has been identified at only one other site in the later Neolithic Alpine Foreland (Central Europe around the Alps), with leafy hay remains in a possible 'stall section' of a house and accumulated dung in an associated yard. Evidence for the presence and foddering of animals in settlements coincides with evidence for dairying from the mortality curves in the region." - Neolithic Farming in Central Europe.
And in case you want a firm date, the Neolithic age in Europe is understood to be about 3500 BCE and older, well before the medieval "dark ages" period AND well before the Roman Empire and Greek city-state world.
Keep in mind too, pre-Roman Northern Gaul was not part of the mediterranean, but it too was still a settled agrarian society, with animal husbandry.