The Roman empire grew and prospered unprecedented by combining exemplary organization, technological advances and military skills with fortunate climate in its 'Golden Age', virtually unifying the Mediterranean world under its 'Pax Romana'. Then it even coped with a major pandemic, possible small pocks, wiping out several over its about 50 million inhabitants. Having stabilized its expanse towards Rhine and Danube, it suffered the effects of worse climate, causing major Germanic and other migrations from the east and north and weakening it as did the much worse pest pandemic, which lay demographic waste to whole cities and regions and kept reemerging all the feudal age, while political stability was shredded by rival generals engaging in coups and civil wars. Medical ignorance -even some counterproductive therapy, despite some progress, both record by physician Galen- causes some great achievements like the baths and sewer systems, to facilitate the spread of germs and diseases, especially in growing cities, most of all the capital, first in Europe to surpass a million people until Victorian London, dependent on huge food imports and unable to drain he marshes breeding malaria mosquitoes.