Neli Miteva (THRACIA, 8, pp. 12-16, Аcademia Litterarum Bulgarica, Serdicae, 1988)
Greek and Roman authors were interested in the Thracians insofar as they associated them with the policy of the Greek world, of Rome and even of Macedonia under Philip II and Alexander the Great. This character of their interest led to reiteration of already established characteristics concerning the Thracians and the "Barbaric" world in general. Even when they were not hostile or biased, these characteristics archaized the actual development of the Thracians.
After the political crisis in Thrace in the 4th-3rd century B.C., the interest of the Roman authors toward its inhabitants was prompted by the aggressive intentions and actions of Rome. This interest did not result in understanding of the actual development of the Thracians: Serdoi, Maidoi, Dentheletoi and Bessi were tribes that were more or less brave, being either allies or adversaries of Rome. The ethnonyms "Bessi" and "Dakoi" (Dacians) gained popularity in historical literature during that period, due to their opposition to the Roman legions. Their aspirations for freedom were sufficient reason for Strabo to qualify the Bessi as bandits, while the Dacians are ferrocious in Horatius' Odes. 
The names of the Roman provinces formed in the Thracian lands are based on onomastic data. These names facilitate the superficial interest of the Roman authors in the ethnic characteristics of the population of the Thracian lands. The Thracians were already subjects of the Empire at that time; after Caracalla's Edict of 212 B.C. they were simply Romans legally before the official rule. The Roman authors confused the traditional idea about the tribal division of the Thracians with the new administrative division, and without being interested in the influx of military and civil persons with different ethnic appurtenance, they characterized the population in the different provinces as Moesians, Dacians, Thracians and Macedonians. However, when they were interested in the actual ethnic belonging of the tribes, they could have been more specific, if they had had the necessary information.
Under the influence of the views of Pliny the Elder on the name "Scythians", the eminent 3rd century historian Dexippus referred to the "Barbarians" attacking to the south of the Danube, led by the Goths, with the collective ethnicon "Scythians."  This name was widely used by the Byzantine authors even after the 12th century.  The tendency towards archaization in this name is combined with the impossibility to specify the ethnic composition of the invaders, which was extremely varied.
When Dexippus and later the 4th century authors — Eusebius, Eunapius, and Philostorgius — who used him as a source, identified "Scythians" with "Goths", this did not exclude at all the real participation of other ethnic groups in the incursions, but reflected the military and political supremacy of the Goths. 
The reforms of Diocletian and Constantine I led to the emergence of the Thracian province by the name of Scythia. The Church historian of the first half of the 5th century B.C. Sozomenes uses the qualification of "the manly Scythians" mainly to denote the inhabitants of Tomis. When he referred to the Bishop of Tomis Theotimus (ca. 392-402) as "Scythian", he did not have in mind his Gothic origin, but the fact that Tomis belonged to Scythia Minor.  The pagan historian Zosimus called the Visigoths "Transdanubian Scythians", the Ostrogoths led by Odothaeus — "Scythians".  Priscus the Thracian mentions that the military leader of Gothic origin Plinthas is of "Scythian origin". This author prefers the archaic ethnicon "Scythians", because it was difficult for him to specify the ethnic composition of Attila's tribal union. Priscus even noted that the "Scythians", i. e. Attila's subordinates, were a conglomerate of different peoples. He used the term "Basileus of the Huns" for Attila, but guided by the tendency toward archaization, he called Attila and Bleda "the royal Scythians." 
The Church historian Philostorgius, and after him Cassiodorus and Jordanes, also used the name "Getae" to denote the Goths — apparently due to phonological similarity and archaization on an ethnogeographic basis. For the Gothic historian Jordanes it was essential to glorify the ancient origin of the Goths through the deeds of the Getae — valiant and numerous horsemen-archers, according to Thucydides, and victors over Lysimachos, according to Diodorus. In the 1st century B. C., led by Burebista, they imposed their hegemony over the Greek colonies and transferred their activities even to the south of the Haemus.
It seems that the chronicler of the first half of the 6th century Marcellinus Comes used the name "Getae" rather arbitrarily, when he did not know the ethnic belonging of someone. The identity between "Getae" and "Slavs" is almost certain, and in the invasion of 530 he differentiated well the "Getae" from the Bulgarians. Identity between "Getae" and Slavs is also found in Theophylactus Simocatta. 
The principal written source about the "Barbaric" incursions into the Thracian lands during the second half of the 3rd century, Historic, Augusta, is of a rather disputed value.  The best 4th century historian, Ammianus Marcellinus, who was a follower of the style of Tacitus, was familiar with the Thracian lands. However, his interest in the ethnic composition of the population of these lands was also superficial. In his tendency toward archaization, he defined "the belligerent tribes of Thrace" as the main force in the rebellion of Procopius in 365-366. "The Bessi were the most severe of these tribes" and "the Hebros descended from the mountains of the Odrysae." 
Claudianus, the poet at the royal court of the West Roman Emperor Honorius, apparently possessed less information about the Thracians. In spite of his panegyric tone, Claudianus rendered correctly the political events in the Balkan Peninsula in his poems, although the ethnic picture that he created was strongly archaized. The Thracians are belligerent tribes; since the Vandal Stilicho, guardian of the minor Emperor Honorius, clashed with the Visigoths of Alaric near Epirus at the end of the 4th century, Claudianus mentioned the Bistones. According to the mythographic tradition, the Bistones were the most belligerent Thracian tribe and Herakles fought against them. This allusion is not accidental — the confrontation was the result of the behind-the-scene struggles between the actual ruler in the eastern half of the Empire, Rufinus, and Stilicho, for conquering the dioceses Dacia and Macedonia. The king of the Bistones, Diomedes, son of Ares, possessed the horses that were lethal for the foreigners. 
In Hieronymus, who was connected with the Church, the apocalyptic picture of the Barbaric devastations in the Balkan lands to the south of the Danube was complemented by the triumph of Christianity. In addition to the other peoples "clad in furs", he also mentions the "wild Bessi" who were subdued for the first time by the force of the Cross. 
The change brought about among the Bessi by Christianity is described in even greater detail by Bishop Paulinus Nolanus in a poem praising the missionary work of Niceta, Bishop of Remesiana (Dacia Interior) at the end of the 4th. century. The "Getae" mentioned by him could have been Alaric's Visigoths who were temporarily stationed in Dacia Ripensis as federates. After Trajan's Dacia was abandoned in the second half of the 3rd century, the interest of the Roman authors in the indigenous population to the north of the Danube vanished completely. Only the "Barbarians", wandering or settled, were mentioned there. After the 3rd century there no longer appeared evidence about incursions of the Carpae to the south of the Danube. The last reference to the "Carpodacians" appears in Zosimus in connection with their unsuccessful attempt to penetrate in the Empire after the year 381. After the compensatory formation of the two provinces Dacia Ripensis and Dacia Interior (south of the Danube) at the end of the 3rd century, for the Roman authors "Dacians" were the inhabitants of these provinces. Paulinus Nolanus also uses the ethnonym in this way. 
Also traditional and influenced by the provincial division is the evidence of the Late Roman military writer Vegetius about the belligerent Dacians, Moesians and Thracians, among whom even Mars was born, and about the Bessi who were industrious miners. 
In the 5th century the Eastern Roman Empire has its excellent historiographers — Priscus and Malchus — who were moderately critical to the rule of the Empire and were tolerant to the "Barbaric" world of Huns and Ostrogoths.  Priscus used the name "Romaioi" for the subjects of the Empire, but this does not prevent him from specifying the ethnic characteristics, whenever that was necessary and possible. The Romaian military leader Dionysius was also of "Thracian origin."  He specified about the merchant captured by the Huns in the "Moesian city of Viminatium" that he was "of Greek origin".  For Malchus the Rhodope area devastated by the Ostrogoths was the "land of the Thracians" due to the tradition in the historic literature and because the Rhodope province was included in the Thracian diocese. 
Of prime importance is the information provided by the Gothic historian Jordanes, who worked around the mid-6th century, about the migration of the ethnic groups after the disintergation of Attila's union in the mid-5th century and about the settling of some of them in the Thracian lands. He also speaks about the secluded existence of the so-called "Gothi minores" in the mountainous area of Nicopolis ad Istrum even in the 6th century. 
The authors after the 5th century (Jordanes, Euagrius, John Malala, Procopius, Theophylactus Simocatta, John of Antioch, and Theophanes) noted the Thracian origin of a number of Emperors of the Romaioi from the second half of the 5th to the beginning of the 7th century (Marcianus, Leo I Bessus, Justin I, Justinian I, Justin II, Tiberius, and Phocas), of eminent Byzantine military leaders (mainly in Procopius, Theophylactus Simocatta and Euagrius). With few exceptions, these authors were very well informed, although it is very natural for their times that they were interested not in the ethnic composition of the population but in the life of prominent individuals. In order to glorify the courage and the ancient origin of Attila's victor, Aetius, born in Durostorum, Jordanes associated him with the Moesians who were known in Homer to be excellent fighters at a close range, in addition to being fearless against the Romans, according to Dio Cassius in his Roman History.  Procopius also mentions the bravery of the Moesians in battle through Homer's verse. Being the best 6th century historian, Procopius gives the greatest number of examples related to the Thracians (either as ordinary soldiers or as military leaders in the Byzantine army). Without going into analysis or enumeration here, it is necessary to mention Procopius' sufficient competence in determining the ethnic appurtenance not only of the Thracians.  He uses the name "Romaioi" as a collective term for the subjects of the Empire. Since in that concrete case Procopius was interested in the military qualities of the representatives of the different ethnic groups in the Byzantine army, he also specified their ethnic characteristics.
Procopius' works are the most important source about the character of the Slav and proto-Bulgarian presence in the Thracian lands during the reign of Emperor Justinian I. Procopius' inofficial criticism in Hisforia arcana is very malicious, being intensified by the exaggerated picture of the devastations and depopulations in the Balkan lands as a result of the Slav and proto-Bulgarian ("Hun") attacks. Emperor Justinian I was held responsible for everything, including earthquakes and floods. Unlike Marcellinus Comes, Procopius already refers not to "Getae" but to Slavs and Antae. He probably learned about their life to the north of the Lower Danube from the Antae in the army of Velesarius. For Procopius the proto-Bulgarians were Huns, which is perfectly natural after the awe-inspiring fame of the Huns and the inclusion of various ethnic groups in Attila's union, among which there were proto-Bulgarians, as well.
The decisive ethnic and social changes in the Thracian lands in the
7th century totally diminished the interest in the fate of the indigenous
population in the scarce evidence of the Byzantine annalists for the 7th
to 9th centuries.
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12. Euseb. Hielonym. Epist. (Migne PL, XXII-XXX) LX, 4.
13. P a u l i n. N o l a n. (Hartel) Carm. XVII, v. 249 sq.; Z o s. (Bonn.), p. 213 sq.
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16. E x c e r p t a de leg. I, 1, p. 122, 12.
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18. Excerpta de leg. I, 1, p. 169.
19. Iord. Get. 259 sq.
20. Iord. Get. 176.
21. У д а л ь ц о в а, З. В. Op. cit., p. 187 sq.