Drake notes that the “one unwritten, but never to be violated, rule of the game of empire was this: although the Senate could be alienated with impunity so long as the loyalty of the troops was secure, it was impossible to alienate both Senate and military and still survive.”

It’s a rule that Nero violated: “Alienated from both Senate and army, Nero took his own life in June 68,” and his death “triggered a constitutional crisis.” No successor was available, and “senatorial and military criteria clashed head-on. On this occasion it was the armies, ever lurking behind the facade [of imperial deference to the Senate], which prevailed. In the course of a single year, A.D. 69, four different men, each backed by a different army, held the title of emperor. Tacitus later said that the ‘Year of the Four Emperors,’ as it was thereafter known, revealed the ‘secret of empire’ . . .

“As he defined it, the ‘secret’ was that ‘emperors could be made elsewhere than at Rome.’” That is, Emperors could be made anywhere there was a strong and restless army: “The revolt of the frontier armies revealed just how few cards the Senate actually held.”

A historical and an eschatological comment: The historical is that this secret was most especially revealed in the third century, and its the secret behind the ascent of Constantine; the eschatological note is to mark the date, and to think of stars falling from heaven and moons turning to blood before the great and terrible day of the Lord . . . .