In his speech On Imperial Rule (or On Monarchy), Synesius of Cyrene offers some advise to the emperor Arcadius (r.395-408). More information about this speech, together with a brief summary, can be found here.
Throughout this speech, the word "Scythians" refers to the Tervingian Germans (who would later be known as Visigoths), whereas "king" refers to emperor.
The text is offered here in the translation by A. Fitzgerald. The four-digit numbers are page numbers of the Migne edition.
On Imperial Rule 2
  Cyrene sends me to you to crown your head with gold and your spirit with philosophy; Cyrene, a Greek city of ancient and holy name, sung in a thousand odes by the wise men of the past,note[E.g., Pindar, Pythian Odes 4, 5, 9; Callimachus, Hymn 2.73, and Epigram 21.2.] but now poor and downcast, a vast ruin, and in need of a king if perchance she is to do something that maybe worthy of her ancient history. This very need you can remedy whenever you so desire, and it is for you to decide whether I shall bring back to you a second crown from my great and then happy city. Words now are not failing to a city wherewith it may have liberty of speech and may dare to address its sovereign boldly. Truth is the aristocracy of language and no word was ever more shameful or more honorable according to the place of its utterance.
  Let us advance in company with God, and let us attempt the fairest of language or, to speak with more truth, the fairest of deeds. For he who cares for one man and that one the king, devising how he may be most virtuous; that man I say has made the shortest step towards restoring all houses, all cities, and all nations, whether great or small, near or far; for of necessity all of them must profit by the condition of the soul of their king. Is it your will then that we proceed in this wise at first, in order that you may bear with my discourse to the end?
 It were wise not to affright the quarry beforehand.note[Plato, Lysis 206a.] Let us enumerate then what things a king should do and what things he should not do, contrasting the base with the noble. Now attend to those things on each side and whenever you recognize that which is worthy, rejoice in it then as your portion adjudged to you by Philosophy, but dismiss the other and determine always to do the one thing and never again the other.
 But if in the course of this address some act of yours appears one of those which we know to be wrong and which you so recognize yourself, in that case you should show your anger with yourself and blush because that has come to light which is not worthy of you. Assuredly this color promises that virtue which comes from a change of mind, for this shame is divine and so seems to Hesiod. But he who is obstinate in his faults, who is ashamed to confess an error, does not gain knowledge from repentance nor does he need healing words;note[Aeschylus, Prometheus 378.] nay, a wise man would say that he should be punished. Thus, methinks, is philosophy from the beginning rough and intractable.