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 8
  Now we must keep guard over ourselves, and that with our whole understanding. We must if possible employ all the weapons in the court for the purpose that flattery may not slip in wearing the mask of friendship, for by this one thing is royalty plundered, however vigilant the guards. For flattery enters, unless the place be thoroughly defended, far within the treasure-chamber, and attacks the most lordly possession of kings, the soul itself; and the more easily, that love of his comrades is not the least virtue in a monarch.
 It was this quality, at all events, that made Cyrus "the pre-eminent"note and Agesilaus the most renowned of kings amongst Greeks and foreigners. He will then learn what course to pursue,  and amongst his friends will make his opinion prevail, but he stands in need of many hands that action may follow.