Policraticus

[2] Though it takes up a wide variety of ethical questions, it is most famous for attempting to define the responsibilities of kings and their relationship to their subjects.

The title Policraticus, like those of other works by John of Salisbury, is a Greco-Latin neologism, sometimes rendered as "The Statesman's Book".

The topics of the books are as follows: John drew his arguments primarily from the Bible and from Roman law, especially Justinian's Code and Novels.

[6] Purportedly following a manual by Plutarch titled the Institutio Traiani [it]—likely invented by John himself—he argued that the prince had four principal responsibilities: to revere God, adore his subjects, exert self-discipline and instruct his ministers.

John's examples of tyrants included the scriptural figures of Sisera and Holofernes, as well as the Roman emperor Julian the Apostate, who attempted to restore Rome's pagan religion.

The beginning of the preface to Denis Foulechat’s French translation of John of Salisbury's Policraticus . 14th century manuscript.
The murder of Julius Caesar - an incident discussed in Polycraticus . From a 1474 incunable .