During the reign of what is called the "Five Good Emperors" (96 A.D. - 180 A.D.), the Roman Empire reached its territorial, economic, and cultural zenith. The five good emperors (Nerva, Trajan, Hadrian, Antoninus Pius and Marcus Aurelius) were known for their moderate policies, in contrast to their more tyrannical and oppressive successors. This period was particularly notable for its peaceful method of succession, whereby each emperor chose his successor by adopting a heir. This prevented the political turmoil associated with emperors both before and after this period. The Empire, secure from both internal and external threats, prospered under the reign of the "good" emperors. This time period of peace is often referred to as the Pax Romana ("Roman Peace"). With the conquest of Dacia during the reign of Trajan, the Empire reached its peak of territorial expansion. At its height, the Roman Empire spanned an area of some 2.5 million square miles (6.5 million sq. km). | 
