This is an open access title distributed under the terms of the prevailing CC-BY-NC License at the time of publication, which permits any non-commercial use, distribution, and reproduction in any medium, provided no alterations are made and the original author(s) and source are credited.Cover illustration: Reconstruction by H. Mylius of building VI, interpreted as a granary, on the Köln-Müngersdorf villa (extracted from F. Fremersdorf,