I usually avoid replying to comments. I feel everyone deserves an opinion and open discussion is good.
But I did want ensure that the facts are correct concerning the reign of the early emperors.
The Pax Romana spanned 16 emperors over 207 years, which would make the average reign around 13 years. A few emperors had very short reigns bringing that average down, but 9 of the 16 ruled for over 10 years and 6 of the 18 ruled for over 15 years. It was considered a period of great stability for the Roman empire and many pinpoint the death of Aurelius as the beginning of the end.