population declined. The economic prosperity of the Roman Empire notwithstanding, the conditions were propitious for a pandemic. The population was unhealthy. About 20 percent of the population—a large percentage by ancient standards—lived in one of hundreds of cities; Rome, with a population estimated at one million, being the largest. The cities were a "demographic sink" even in the best of times. The death rate exceeded the birth rate and a constant in-migration of new residents was necessary to maintain the urban population. As perhaps more than one-half of children died before reaching adulthood, the average life expectancy at birth was only in the mid-twenties. Dense urban populations and poor sanitation contributed to the dangers of disease. The connectivity by land and sea between the vast territories of the Roman Empire made the transfer of infectious diseases from one region to another easier and more rapid than it was in smaller, more geographically-confined societies. Epidemics of infectious diseases in the empire were common with nine recorded between 43 BCE and 148 CE. The rich were not immune to the unhealthy conditions. Only two of emperor Marcus Aurelius's fourteen children are known to have reached adulthood. A good indicator of nutrition and the disease burden is the average height of the population. The conclusion of the study of thousands of skeletons is that the average Roman was shorter in stature than the people of pre-Roman societies of Italy and the post-Roman societies of the Middle Ages. The view of historian Kyle Harper is that "not for the last time in history, a precocious leap forward in social development brought biological reverses." Spread of the disease The traditional Roman view attributed the cause of the Antonine plague to the violation by the Roman army of a temple in the city of Seleucia and carried back to the Roman Empire by soldiers. However, the first documented case of the plague was in Smyrna in 165 where the orator Aelius Aristides almost died from the disease. From the east the plague spread westward reaching Rome in 166 and nearly every corner of the empire by 172. The co-emperor Lucius Verus died from the plague in 169 and it ravaged the Roman army. The plague endured until about 180 and another epidemic, possibly related, is reported by Dio Cassius to have struck the city of Rome in 189. Two thousand people in the city often died