History of the Roman Empire founder of the brief Flavian dynasty, to be followed by the Nerva–Antonine dynasty which produced the "Five Good Emperors": Nerva, Trajan, Hadrian, Antoninus Pius and the philosophically inclined Marcus Aurelius. In the view of the Greek historian Dio Cassius, a contemporary observer, the accession of the emperor Commodus in 180 AD marked the descent "from a kingdom of gold to one of rust and iron"—a famous comment which has led some historians, notably Edward Gibbon, to take Commodus' reign as the beginning of the decline of the Roman Empire. In 212, during the reign of Caracalla, Roman citizenship was granted
Historiography of the fall of the Western Roman Empire the cities, which became overpopulated. Roman cities were only designed to hold a certain number of people, and once they passed that, disease, water shortage and food shortage became common. Publishing several articles in the 1960s, the sociologist Seabury Colum Gilfillan advanced the argument that lead poisoning was a significant factor in the decline of the Roman Empire. Later, a posthumously published book elaborated on Gilfillan's work on this topic. Jerome Nriagu, a geochemist, argued in a 1983 book that "lead poisoning contributed to the decline of the Roman empire." His work centred on the level to which the ancient