The significance of malaria for the decadence and the final fall of the Western Roman Empire is discussed controversially. It seems verisimilar that Central Europe was free of malaria at the end of the last ice age, and it is undisputed that the Apennine peninsula was a substantially depopulated, endemic malaria area around 600 A.D. The immigration of three of the four Plasmodium species infectious for man took place most likely at different era and with very different effects on the antique societies. A text passage in the Digesta of Justinian (D 21.1.1.8), written by the post classical jurist Ulpian (approx. 170-223 A.D.), illuminates selectively in region and period the malaria situation of the social underclass in and around Rome, a city with a population over a million at that time. The quotation indicates, shortened, "that an old Quartana, about which one does not have to worry any longer, is not an argument for a warranty for defects in case of slaves bought at the market". From this annotation one can deduce that at the turn of the second to the third century A.D. Quartana recrudescence represented the medical normality for people from the social underclass in Rome and the surrounding area. Thus, while at that time Plasmodium malariae seemed to be a common part of the human parasite fauna in Latium, Malaria tropica and Malaria tertiana did not yet unfold their depopulating, economically and socially devastating effects; this happened several centuries later, although the existence of at least one effective vector is proven.