Synesius, On Imperial Rule 18
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 18
  First of all, let the soldiers be enjoined to show consideration to the city populations, and to the rural also, and to be as little as possible a burden to them, remembering the duties they have undertaken on their account. For the king fights in their defense, and enlists men to fight in order that the prosperity of the town and the countryside may be preserved.
 Whosoever, therefore, keeps the foreign enemy from me, but does not himself treat me with justice, such a man as this seems to me in no wise to differ from a dog who pursues wolves as far away as possible for no other reason than that he may himself slaughter the flock at his leisure, whereas in his fill of milk he has received the due reward of his guardianship.note[Plato, State, 416e 464c.] True peace, therefore, comes if the soldiers have been trained to treat civilians as brothers, and only to take what the regulations permit.