In his speech On Imperial Rule (or On Monarchy), Synesius of Cyrene offers some advise to the emperor Arcadius (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 3
  Now, inasmuch as I perceive that some you are already disconcerted and take in dudgeon my freedom of speech, let such remember that I announced this as my intention beforehand, and that it was rather their part, as men forewarned, to arm themselves in defense, and to hold their ground against my attacks. None the less you may rejoice in hearing these things that are to follow, for all men are proclaiming them.
 And I, too, agree with you, that so great an empire has been accorded to no one man nor such an agglomeration of wealth, beyond that of Darius of old, nor yet so many myriads of horse, of archers and cuirassiers. Against such men as these, if only they have the fortune to find a leader, every attack is impotent. Moreover, cities defying computation bow before you, the greater part of which have never beheld you, nor have even hope of beholding a sight that is indeed beyond their aspirations. These truths must be stated to you by us rather than by anyone else.
 What quality then do we possess that they do not share? While they, forsooth, weave praises for you for these very things and proclaim you happy, I would never praise you in consequence of things such as these. I should offer you my best congratulations. But they are not of one and the same nature, congratulations and praise. Each of them differs from the other. For a man is congratulated on possessions external to himself, but he is praised for his inward gifts, thosenote[Aristotle, Nicomachean Ethics 1.12.] upon which happiness has her throne. The one is an uncertain gift of fortune, the other a personal virtue of character.note[Philo, Embassy to Gaius 1.] In this way the latter is of itself trustworthy, but good fortune is deceptive and often changes to that which is completely opposite. But God himself s needed for a guardian, mind is needed, skill is needed, opportunity is needed, and in sooth many works, in many places and these of all sorts, of which one has no experience, nor is it easy for those who try to gain it. For not so easily as a happy condition comes to men, is it preserved.
 You have only to observe in what manner of lives the scenes of the tragedies are cast.note[Dio Chrysostom, Discourse 13 20.] They are not those in which private citizens and the poor suffer, but rather the strong, the potentates, the monarchs. For the modest house has no room for the greatness of disaster, nor poverty for the burden of misfortune; but he who is a shining object in his fortune is fated to become also conspicuous in perils and in the other spheres of the demon's activity. But ofttimes, too, virtue has been the beginning of good fortune, and approbation has been the leader of happiness to men,note[Aeschines, False embassy 131.] as though Fortune were ashamed not to bear witness to conspicuous virtue.
 Now if we are required to make this truth convincing by examples, let us not seek the proof elsewhere. We have to ponder over your sire, and you will see that his Empire was given him as a recompense for his virtue. Fortune is not responsiblenote[Philo, Embassy to Gaius 1.] for virtue, but some virtuous deeds, perhaps, have ere drawn even fortune with them. With these deeds, my liege, may you be associated, that philosophy may not speak here in vain! May rule be a sacred possession to you in this, that it has trained you virtue and has brought it forward in quest of material adequate to its inborn greatness, and not incapable of being contained in a principle of life less than the kingly.
 You must therefore train yourself to keep up a spirit worthy of a king and you must make a defense on behalf of Fortune, that she may not be indicted for lack of reason on the ground that life has not advanced from like beginnings for your sire and for yourself. For him the soldier's art procured the control of Empire, you that Empire enlists as a soldier and virtue is your debt to Fortune. He acquired his possessions by his labors, but you without labor have come into the heritage of these. There is all need of labor to keep guard over them. This is what I have long been speaking of, this the thing of difficulty which needs a thousand eyes, lest, as is Fortune's wont, she may turn back in the midst of the way, like knavish fellow-companions of a journey, for to such do the wise compare inconstancy. You see in the case of your own sire so clearly proclaimed in public by reason of his successes, that envy did not suffer even his old age to pass without struggles, nor yet the Divinity without a crown. After marching against two usurpersnote[Magnus Maximus (383-388) and Eugenius (392-394).] and overthrowing both, on erecting the second trophy, he gave up his life, slain by the hand of no man, but yielding to Nature,  against whom neither is weapon strong nor mind skilled, and leaving you the kingdom uncontested, he has virtue as his epitaph. May virtue preserve it for you and may God preserve it through virtue, for there is need of God everywhere and not least amongst those who are not the contestants or architecture of their fortune, but who, like you, inherit it!
 He whom the Divinity has most largely endowed with fortune, and whom, when still a mere boy, He has made to be called a great king, must choose all labor and abandon all ease. He must share little in sleep and much in anxieties, if he is to be a fitting person to be crowned with the name of "king". For well says the old proverb
It is not the number of subjects that makes a king any more than a tyrant."
 In truth the tale of his sheep makes not the shepherd more than the butcher who drives the sheep before him to the slaughter, that he may himself take his fill of them and sell them for a feast to others. Equally divided stand the king and the tyrant,note[Using "tyrant", Synesius does not refer to sole ruler (the normal meaning in Greek), but to a dictatorial ruler. The reference is to Aristotle, Nicomachean Ethics, 8.12.] I assert, and yet Fortune's gifts are alike to each. Each of the two rules over many men, but he that disposes himself for the manifest good of the governed, and is willing to suffer that there may be no suffering for them, and to encounter danger that they may live without fear, and to keep night vigils, and to sup with cares at his board, that day and night they may have rest from anxieties, this is a shepherd amidst his sheep, a king amongst men.
 But whoso exploits his leadership for luxury's sake, whoso squanders his resources in reveling, esteeming that he must needs gratify all his desires, considering that what makes the subject class suffer is the guerdon of his rule among many, and that the pleasure of his soul is to be served by many, and in a word, he who does not fatten his flock, but himself desires to be fattened by it, that man I call a butcher amongst his cattle, and I declare him to be a tyrant whenever that which he rules over is a people endowed with reason.
 Now let this be the one principle of kingship for you, and do you test yourself by it as by a touchstone. If you find yourself in harmony with it, you may with every right enjoy the sacred title of a sacred office; but if you are not in harmony with it, endeavor to make straight what is distorted, and to cling to the rule. I do not despair of every progress coming from youthnote[Plato, Theaetetus 146b.] if only someone may spur it on towards zeal for virtue. For youth is strong in its tendency to one side or the other,note[Philo, Embassy to Caligula 29.] just as rivers in the first stretches allotted them press on the more insatiably. In this way the young king has need also of philosophy, either to take possession of him beforehand or to restrain him from dispersing his force on either side.
  Some vices are near neighbors to certain vices, and from each of these last there is a slip, not into another virtue but into its neighboring vice. Tyranny dwells near kingship, even next door to it, as foolhardiness near to courage, as license to liberty. The high-minded man, if he is not guarded by philosophy within the realm of virtue, will trip and will become a braggart, and one feeble in judgment instead of high-minded. Fear, therefore, tyranny as being nothing else than the disease of kingship, and learn to discern it by the distinctive marks presented in my discourse, and by the greatest of them, that while the law is his conduct for the king, his own conduct is law for the tyrant.
 But power is a substance that they have in common although their lives are antagonistic. Every man treads the heights of good fortune and of happiness when all follows according to his desire, in the course of nature; but desire in turn attends upon prudence, and although she be the mistress of what is without, she yields a share of the kingdom within to the stronger comrade and receives from her the watchwords for necessary action. Power does not suffice for happiness, nor has God placed happiness in strength, but prudence must be present, nay, must be in the first rank, to use such strength in the noblest way.
 Now that man I proclaim to be the most complete, and this is true of his life also, who is perfect in both and not halting in either, the man to whom has fallen the task of ruling, knowing the while how to rule. Strength and wisdom when united are irresistible,note[Plato, State 473d.] but separated from each other, untutored force and prudence shorn of strength will be easily overcome.
 I have always admired that creation of the wise Egyptians, their Hermes. The Egyptians make the face of their deity double, placing a young one next to an old one,note[Cf. Synesius, Egyptian tale 1.11.] requiring thus of anyone who is to keep good guard over them that he be both wise and strong, as the one thing would be useless without the other. In the same way the Sphinx is erected in their temple closes, a sacred symbol of the coupling of virtues, in strength a wild beast, in prudence a man. And rightly, for strength destitute of prudent leadership is carried capriciously along, mingling all matters together and throwing them into confusion.
 On the other hand mind is useless in action when unserved by hands. All virtues are a king's adornment, but prudence is the most kingly of them all. Take to yourself this one, I counsel you, for an associate, for the three sisters will follow the eldest, and you will straightway have them all as comrades in your tent, and on the battlefield as well.