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 13
  And another story more recent than this I think you must have heard, for it is improbable that anyone has never heard of a king who assigned himself the task of getting within the enemy's country for purpose of espionage, by imitating the appearance of an embassy. For it was in those days a duty to the State to take command of cities and armies, and many men foreswore such an office; nay, a certain ruler among them, one who had spent his youth in ruling, renouncing these labors, decided of his own free will to grow old in private life.
 Further, this very title of king, I will show to be recent; for it had become a dead letter to the Romans from the time when the people drove out the Tarquins. For it is from this source that while we call you kings, while we deem you worthy of the title and write you down as such, you, whether you know it or not, yielding to established custom, seem to evade the dignity of the title.note[In Latin, the emperor called himself Augustus or imperator, which was translated into Greek as autokrator, 'absolute ruler'.] An so, when you write to a city, or to an individual, to a viceroy or to a foreign ruler, you have never shown pride in the title of king, but rather you make yourselves absolute rulers.
 Now absolute ruler is the designation of a military ruler who undertakes to do all things, and Iphicrates and Pericles sailed from Athens as generals with absolute power, nor did the title wound that people, free from tyrants though it was; for the people itself made appointments to this generalship, as being constitutional.
 It is true that in Athens there was a certain individual called king who occupied a petty post, and was accountable for his administration; the people, I suppose, having given him this name in jest, for they were an uncompromisingly free people.note[A reference to the official known as archon basileus.]Their 'absolute ruler', however, was not a monarch, and both the title and the office were respected.
 Is not this, then, clear evidence of a wise policy in the Roman constitution, that although it has manifestly developed into a monarchy, it is cautious in so asserting itself by reason of its hatred of the evils of tyranny, and employs the title of king sparingly. For tyranny makes monarchy to be detested, whereas kingship makes it to be loved; and Plato calls this a divine good amongst men.note[Plato, Politicus 302e.] But this same man also asserts that what shares in the divine destiny is in every case free from vanity.note[Plato, Phaedrus 247a.] For God is not theatrical, nor a worker of wonders but
... walking in a noiseless path according
to Justice, he directs mortal affairs.note[Euripides, Trojan Women 887-888 = Plutarch, Isis and Osiris 381b.]
And everywhere He is ready to reveal Himself to that one endowed with a nature to receive Him.
 In this sense I maintain that the king is a common source of good and free from arrogance. But if tyrants are always doing astounding things, concealing themselves from the public gaze, and then appearing to the consternation of the beholders, we cannot envy them,  since in default of true majesty they take refuge in a pretence of it, for in the case of one who has no health in him and is conscious of the fact, what means may there be for his escape from contempt except that of escape from publicity?
 But up to this day no one has ever despised the sun, although to what spectacle are we more accustomed? And if a king has courage to be a true one and shall not be disproved as such, let him be the most common possession; for he will not be the less admirable in this even if he be not the more.
 Further, the lame king whom Xenophon praises throughout all his history was not derided by those whom he led, nor by the nations through whom he led them, nor by those against whom he made his expedition; and yet he lodged in the most public places of each city. Meanwhile he was most conspicuous in all his actions to everyone who desired to see the leader of Sparta. Nay, this man crossed over to Asia with a small army and very nearly succeeded in driving from his kingdom a man receiving homage from numberless people. At all events he drove him from the stronghold of his arrogance.
 And so it happened that when recalled by the magistrates in his own city and compelled to give up his military operations in Asia, he achieved many victories in Greece and was defeated in battle by one man only, by the only man who could possibly overcome Agesilaus were the struggle for frugality.note[The Second Battle of Mantineia in 362, described by Plutarch, Agesilaus 35.] This was that Epaminondas whom cities crowned with wreaths, and invited to banquets. But when he accepted such invitations, for one could not do otherwise than accept without incurring injury to his political reputation, he drank nothing but rough wine, 'in order' - so he said - 'that Epaminondas might not forget his home diet.' And when a young Athenian scoffed at the hilt of his sword because it was made of a cheap sort of wood and uncarven, he replied, 'When we fight, you will not make trial of the hilt, but I do not think you will be able to find fault with the blade.'
 Now if it is kingship to command, and to command with such forces as do those who know upon what things power is based and upon what sort of lives; we see that it is not from what is unnatural and from luxury, but from moderation and wisdom that all things are brought into order from every source. Arrogance and extravagance must be eliminated from kingship, for there is no common ground between it and those things foreign to it; and indeed my discourse started from this very point.