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 14
  Let us now bring back the argument to its proper beginning, and do you bring back the king to his original function. It will follow of necessity that once our lives have been corrected and Prudence has returned,  the glories of the past will accompany her, and a complete change will take place in all the elements opposed to her.
 And do you, my liege, rule over the return of good works, and give us back the king who is a public-spirited servant of his kingdom. In the present state of affairs we can no longer either dally at our ease or make a step in advance, for at present all men are standing on the edge of a razor. We stand in need of God for our affairs and of a king who will avert that destiny of the Roman power which has been long in coming to birth; and while I am abridging the rest of my argument, and at the same time moulding an image of a king which I began to set up as a beautiful statue, I will at least show you clearly that 'this destiny' is imminent unless a wise and strong kingship prevents it in time, and I shall assist you as far as I can in contriving this, to wit, that you may be the one who shall prevent it.
 God is always and entirely the ally of the good, and is propitious to them. So then we have left the common duties of the king as modeled in this discourse and have been brought round in opinion to the established order of things. Philosophy demanded of the king that he should often mix with the military, and not keep to his palace, for it taught us that goodwill towards him, his only real safeguard, was fortified by this daily intercourse.
 This once admitted, in the company of what race of soldiers should a philosopher devoted to his king desire that he should train his body and dwell in the camps? Evidently with such as the countryside and towns, in a word the land he rules over, gives him as fighting men and selects as guards for the State, and for the laws by which they were nurtured and educated, for these are they whom Plato likened even to watchdogs.note[Plato, State 375e.] But the shepherd must not mix wolves with his dogs, even if caught as whelps they may seem to be tamed, or in an evil hour he will entrust his flock to them; for the moment that they notice any weakness or slackness in the dogs, they will attack these and the flock and the shepherds likewise.
 Nor must the legislator give arms to those not born and brought up under his laws, for he has no guarantee of their good conduct from such as these. Truly it is the part of a foolhardy man or of a prophet to see and have no fear of this mass of differently bred youth pursuing their own customs, and at the same time practising the art of war in this country. They must either think all these men to be wise as philosophers; or if they rightly despair of this they must believe that the rock of Tantalus is suspended over the State by fragile cables. For these men will fall upon us the first moment they think the attempt likely to succeed.
 Even now some skirmishes of this sort are manifest and certain parts of the empire are becoming inflamed, as though it were a human body in which alien portions are incapable of mingling in a healthy state of harmony. Then in the case of cities as in that of the body, we must separate the alien parts as the sons of physicians and generals would say.  But not to organize a force to cope with these men, and to grant immunity from military service to many who ask for it, and to allow those in the countryside to devote themselves to other callings, as if that barbarian army were our native production, what is this but the act of men hastening to their doom?
 Rather than allow the Scythians to be under arms here, we ought to seek from the agriculture so dear to them the men who would fight to defend it, and we ought to enroll all these in a military force, to such a point as to summon the philosopher from his study, the craftsman from his lowlier calling, and from the shop its salesman. As to the crowd of drones who pass their lives in the theatres by reason of their unlimited leisure, we should beg of them to make haste for once in their lives, before they should be turned to tears from their laughter; for there is no motive of either the better or the worse shame that shall stand in the way of the Romans possessing a force of their own.
 The same organization holds good for the State as in the family; the male element must defend and the female occupy itself with the care of the household within.note[Plato, Meno 71e.] How then can you endure that the male element should be foreign? Is it not disgraceful that the empire richest in men should yield the crown of glory in war to aliens? For my own part, however may victories such men might win for us, I should be ashamed of the aid so received. This very thing, 'well I know, I do opine'note[Unidentified quotation.] (for it is obvious to any sensible man) that when the male and female of which we speak do not happen to be brother and sister, or in any other way related, the armed portion of them will need but a slight excuse to demand mastery of the civilians, and then the unwarlike will be pitted against those inured to the shock of arms.
 Before matters have come to this pass, one to which they are now tending, we should recover courage worthy of Romans, and accustom ourselves to winning our own victories,  admitting no fellowship with these foreigners, but disowning their participation in any rank.