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 catastrophic: Peter Heather, in his "The Fall of the Roman Empire" (2005), maintains the Roman imperial system with its sometimes violent imperial transitions and problematic communications notwithstanding, was in fairly good shape during the first, second, and part of the 3rd centuries AD. According to Heather, the first real indication of trouble was the emergence in Iran of the Sassanid Persian empire (226–651). As reviewed by one writer on Heather's writing, Heather goes on to state—in the tradition of Gibbon and Bury—that it took the Roman Empire about half a century to cope with the Sassanid threat, which it did