I'd guess that they didn't chill the wort. Seeing that until the mid 1800 they didn't know about yeast I'd be willing to bet they didn't pitch any! Beer ferming was somewhat of a mystery, brew your wort and let it sit for a few days a it would magically start to ferment. Most likely due to airborne yeast spores.
As far as the Lagering goes, caves, either natural or dug out, and deep cellars were how they "lagered" beer (from the German word Lagern, or to store).