1. Philostorgius Ecclesiastical History 3.4 (published about 425)
[Because Philostorgius was openly sympathetic to the Arian branch of Christianity his history was shunned by an increasingly trinitarian literary establishment in the 5th century. But manuscripts must have survived and Photius, the Byzantine patriarch in the second half of the 9th century, left a summary full of disapprobation, but also full of long quotations of which the following is an example. Translated from Greek]

“He (Philostorgius) says that Constantius sent ambassadors to those who were formerly called Sabaeans, but are now known as Homeritae (Himyarites), a tribe which is descended from Abraham by Keturah. As to the territory which they inhabit, he says that it is called by the Greeks ‘Arabia Magna’ and ‘Arabia Felix,’ and that it extends into the most distant part of the ocean. Its metropolis, he says, is Saba, the city from which the queen of Sheba went forth to see Solomon. This tribe is part of the Israelite family, and practises circumcision on the eighth day; but they also offer sacrifices to the sun and moon, and to the native gods of the country. Constantius accordingly sent an embassy to them, in order to induce them to come over to the true religion. The emperor determined, in pursuance of his plan, to conciliate the king of that people by magnificent presents and words of gentle persuasion, and then to take an opportunity right away for sowing the seeds of religion. He also asked for licence to build churches on behalf of the Romans who came there by sea, and the inhabitants of the country who wished to embrace the Christian faith. At the head of this embassy was placed Theophilus ‘the Indian,’ who had been sent when very young as a hostage from the Divaeans to the Romans when Constantine was at the head of the empire. The island called Divus, is a portion of their territory, and the inhabitants of it are called Indians. Further, he relates that this Theophilus, having passed a long life among the Romans, formed his character upon a pattern of the most strict and perfect virtue, and embraced the true faith concerning God; but, he adds, that he chose the monastic life, and was promoted to the diaconate at the hands of Eusebius (of Nicomedia – an Arian luminary). So much for his early life. But afterwards, having undertaken this embassy, he was ordained, by the men of his own faction, to the episcopal dignity. But Constantius, wishing to array the embassy with peculiar splendour, put on board of their ships two hundred well-bred horses from Cappadocia, and sent with them many other gifts, with the double view of making an imposing show and of conciliating the feelings of the people. Accordingly, Theophilus, on his arrival among the Sabaeans, endeavoured to persuade the ruler of the tribe to become a Christian, and to abandon the deceits of heathenism. Then, the falsity and malice of the Jews (anti-Jewish sentiment was intense at this time and Himyar had a reputation for receiving the Jewish exiles fleeing frequent pogroms in the Roman empire) was compelled to shrink into deep silence, as soon as Theophilus had once or twice proved by his wonderful miracles the truth of the Christian faith. The embassy turned out successfully; for the prince of the nation, by sincere conviction, came over to the true religion, and built three churches in the district, not, however, with the money which the emperor's ambassadors had brought with them, but out of sums which he voluntarily supplied from his private resources – he had a praiseworthy desire to compete with the miracles performed by Theophilus. One of these churches he erected in a place called Zaphar, the metropolis of the nation: another in the place where the market of Roman commerce stood, lying towards the outer sea (on the gulf of Aden, modern Oman). This place is called Adane; and it is the spot where everybody is in the habit of landing on coming out of the Roman territories. The third church he built in another part of the district, where the market of Persian commerce stands, hard by the mouth of the Persian Sea, which lies along those parts.”

2. Athanasius Apology to Constantius 30, 31 (357)
[Athanasius was one of the most influential theological voices in framing the trinitarian stance promulgated by the Council of Nicaea in 325, and he went on to be an oft-persecuted bishop of Alexandria. As bishop he took responsibility for the church in Aksum, the leading city of the Ethiopian empire at the southeastern end of the Red Sea. In 356 Constantius had Athanasius removed from his episcopacy thus inspiring the Apology (apologia means legal defense in Greek). George of Cappadocia was sent as official imperial bishop replacement (you met him as the emperor Julian’s tutor). In this work Athanasius quotes two interesting letters sent by Constantius to the citizens of Alexandria and leaders of Aksum respectively. Frumentius is the bishop ordained by Athanasius to oversee the Christian church in Aksum. Translated from Greek.]

Victor Constantius Maximus Augustus to the Alexandrians. Your city, preserving its distinct character, and remembering the virtue of its founders (Alexander the Great and the Ptolemies), has habitually shown itself obedient unto us, as it does at this day; and we on our part should consider ourselves greatly wanting in our duty, did not our good will eclipse even that of Alexander himself. For as it belongs to a temperate mind, to behave itself orderly in all respects, so it is the part of royalty, on account of virtue, permit me to say, such as yours, to embrace you above all others; you, who rose up as the first teachers of wisdom who were the first to acknowledge God; who moreover have chosen for yourselves the most consummate masters; and have cordially acquiesced in our opinion, justly abominating that impostor and cheat, and dutifully uniting yourselves to those venerable men who are beyond all admiration. And yet, who is ignorant, even among those who live in the ends of the earth, what violent party spirit was displayed in the late proceedings? With which we know not anything that has ever happened, worthy to be compared. The majority of the citizens had their eyes blinded, and a man (Athanasius) who had come forth from the lowest dens of infamy obtained authority among them, entrapping into falsehood, as under cover of darkness, those who were desirous to know the truth — one who never provided for them any fruitful and edifying discourse, but corrupted their minds with unprofitable subtleties. His flatterers shouted and applauded him; they were astonished at his powers, and they still probably murmur secretly; while the majority of the more simple sort took their cue from them. And thus all went with the stream, as if a flood had broken in, while everything was entirely neglected. One of the multitude was in power — how can I describe him more truly than by saying, that he was superior in nothing to the meanest of the people, and that the only kindness which he showed to the city was, that he did not thrust her citizens down into the pit. This noble-minded and illustrious person did not wait for judgment to proceed against him, but sentenced himself to banishment, as he deserved. So that now it is for the interest of the barbarians to remove him out of the way, lest he lead some of them into impiety, for he will make his complaint, like distressed characters in a play, to those who first fall in with him. To him however we will now bid a long farewell. For yourselves there are few with whom I can compare you: I am bound rather to honour you separately above all others, for the great virtue and wisdom which your actions, that are celebrated almost through the whole world, proclaim you to possess. Go on in this sober course. I would gladly have repeated to me a description of your conduct in such terms of praise as it deserves; O you who have eclipsed your predecessors in the race of glory, and will be a noble example both to those who are now alive, and to all who shall come after, and alone have chosen for yourselves the most perfect of beings as guide for your conduct, both in word and deed, and hesitated not a moment, but manfully transferred your affections, and gave yourselves up to the other side, leaving those grovelling and earthly teachers, and stretching forth towards heavenly things, under the guidance of the most venerable George , than whom no man is more perfectly instructed therein. Under him you will continue to have a good hope respecting the future life, and will pass your time in this present world, in rest and quietness. Would that all the citizens together would lay hold on his words, as a sacred anchor, so that we might need neither knife nor cautery for those whose souls are diseased! Such persons we most earnestly advise to renounce their zeal in favour of Athanasius, and not even to remember the foolish things which he spoke so plentifully among them. Otherwise they will bring themselves before they are aware into extreme peril, from which we know not any one who will be skilful enough to deliver such factious persons. For while that pestilent fellow Athanasius is driven from place to place, being convicted of the basest crimes, for which he would only suffer the punishment he deserves, if one were to kill him ten times over, it would be inconsistent in us to suffer those flatterers and juggling ministers of his to exult against us; men of such a character as it is a shame even to speak of, respecting whom orders have long ago been given to the magistrates, that they should be put to death. But even now perhaps they shall not die, if they desist from their former offenses, and repent at last. For that most pestilent fellow Athanasius led them on, and corrupted the whole state, and laid his impious and polluted hands upon the most holy things.

Constantius Victor Maximus Augustus, to Æzanes and Sazanes (leaders of Aksum). It is altogether a matter of the greatest care and concern to us, to extend the knowledge of the supreme God ; and I think that the whole race of humankind claims from us equal regard in this respect, in order that they may pass their lives in hope, being brought to a proper knowledge of God, and having no differences with each other in their enquiries concerning justice and truth. Wherefore considering that you are deserving of the same provident care as the Romans, and desiring to show equal regard for your welfare, we command that the same doctrine be professed in your Churches as in theirs. Send therefore speedily into Egypt the Bishop Frumentius to the most venerable Bishop George, and the rest who are there, who have special authority to appoint to these offices, and to decide questions concerning them. For of course you know and remember (unless you alone pretend to be ignorant of that which all men are well aware of) that this Frumentius was advanced to his present rank by Athanasius, a man who is guilty of ten thousand crimes; for he has not been able fairly to clear himself of any of the charges brought against him, but was at once deprived of his see, and now wanders about destitute of any fixed abode, and passes from one country to another, as if by this means he could escape his own wickedness. Now if Frumentius shall readily obey our commands, and shall submit to an enquiry into all the circumstances of his appointment, he will show plainly to all men, that he is in no respect opposed to the laws of the Church and the established faith. And being brought to trial, when he shall have given proof of his general good conduct, and submitted an account of his life to those who are to judge of these things, he shall receive his appointment from them, if it shall indeed appear that he has any right to be a Bishop. But if he shall delay and avoid the trial, it will surely be very evident, that he has been induced by the persuasions of the wicked Athanasius, thus to indulge impiety against God, choosing to follow the course of him whose wickedness has been made manifest. And our fear is lest he (Athanasius) should pass over into Aksum and corrupt your people, by setting before them accursed and impious statements, and not only unsettle and disturb the Churches, and blaspheme the supreme God, but also thereby cause utter overthrow and destruction to the several nations whom he visits. But I am sure that Frumentius will return home, perfectly acquainted with all matters that concern the Church, having derived much instruction, which will be of great and general utility, from the conversation of the most venerable George, and such other of the Bishops, as are excellently qualified to communicate such knowledge. May God continually preserve you, most honoured brethren.

3. Codex Theodosianus 12.12.2
[The CT represents a monumental compendium of jurisprudence from 312-438 sponsored by the emperor Theodosius II and made the law of the empire in 439. In the following cryptic edict Constantius appears to want to rebuke his ambassadors/agents working in Aksum and Himyar. Strategius Musonianus was the praetorian prefect of the east from 354-358. The 15th indiction goes from September 1, 356 to September 1, 357. Julian was first consul from January 1, 356 to December 31, 356. Translated from Latin]

Emperors Constantius and Constans augusti and Julian to Musonianus praetorian prefect: No one commanded to visit the peoples of Aksum and Himyar should delay more than one year in Alexandria nor should he draw travel allowances beyond one year. Given Jan 15 from Milan in the 15th indiction with Constantius and Julian as consuls