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 16
  Now the warlike king may be above all a man of peace, for to him alone who is able to inflict injury upon the evildoer is it given to keep the peace. For my own part I should say that the king has, all in all, gained most applause as a peacemaker who, although desiring injustice to none, is nevertheless provided with the power to escape injury at the hands of others; for if he does not war, he will certainly be warred against.
 Peace is a happier state than war, because the preparations of war are actually made with a view to peace. The end in view would justly be preferred to those things which exist on its account. Thus it is well that the king give himself up to each half of his command in turn, that body politic divided into two estates, that of the armed men and that of the unarmed; and after consorting with his fighting men, he should visit cities and country districts to which, by the use of the military, we have granted fearless possession of their farms and civic rights.
 He will visit again and again in his tours as many races and as many cities as possible; and whatever portion of his Empire he does not reach, even to that he will devote his attention in what is apparently an effective and excellent way.