The Odrysian kingdom was founded by king Teres I, exploiting the collapse of the Persian presence in Europe due to failed invasion of Greece in 480–79.

[3] Said historians considered the Thracians to be a numerous people and their country, Thrace, to be of barely comprehensible size, so large that Andron of Halicarnassus (4th century BC) thought of it as a continent of its own.

Northern Thrace was defined by the Danube, the Carpathians and the adjacent western tip of the Pontic–Caspian steppe, thus enclosing parts of the territory now comprising modern Romania, Moldova, Serbia and Ukraine.

[10] The absence of imported artefacts confirms that inland Thrace north of the Rhodopes remained largely isolated from the Aegean trade until the late 6th century.

[11] In around 513 BC, an army of the mighty Persian dynasty of the Achaemenids crossed the Bosphorus, after already having subdued the Thracians of Bithynia thirty years earlier.

[13] It seems most likely that the Achaemenids did not establish a satrapy (provincial administration) in Thrace,[12][14] even though the historian Herodotus claimed that the subdued regions had to pay taxes.

[14] Writing in the late 5th century BC, he wrote that Teres "was the first powerful king of the Odrysae" and that he "was the first founder of the great Odrysian empire, which he extended over a large part of Thrace, although many of the Thracian tribes are still independent.

[24] Around the middle of the 5th century, when Sitalces had not yet succeeded his father,[25] the Odrysians intervened in a Scythian civil war, seemingly on the side of the dethroned king Scylas against Octamasadas, who was a son of Ariapeithes and Teres' sister.

When the two armies met at the Danube, however, Sitalces simply agreed to hand over Scylas (who was killed on the spot) for an unnamed brother of his who resided among the Scythians.

[27] Archaeological evidence confirms that by the middle of the 5th century BC, a new and powerful elite had emerged that accumulated a wealth of precious artifacts of both local and regional origin.

[34] Now, his influence extended over much of Bulgaria, Greek and Turkish Thrace and also parts of southeastern Romania: from the Strymon and Iskar rivers in the west to the Black Sea and the Propontis in the east as well as the Haemus and the mouth of the Danube (which was ruled by the tributary Getae) in the north.

[36] Sitalces, apparently an experienced leader with political acumen,[40] would prove his commitment to the alliance in the next year, when he arrested a Peloponnesian embassy that tried to persuade him to join the Spartan side and handed it over to Athens.

[36] While Sitalces managed to subjugate some of the Thracian tribes of the lower Strymon, his invasion of eastern Macedon and the Chalkidiki was less successful, as his opponents avoided open combat and simply hid behind their walls.

In 400 BC he hired Greek mercenaries under Xenophon to expand his dominion at the cost of Teres and other rebels, forcing them to reacknowledge the authority of Amadocus.

In 389 the Athenian general Thrasybulus mediated between the two parties, resulting in Seuthes II, whom Xenophon called "ruler of the coast region", recognizing Amadocus' authority again.

[63] As early as 359, the year of his coronation, Philip II of Macedon I contacted a "Thracian king" to persuade him to not harbour a Macedonian pretender to the throne.

[71] As a result of this campaign[72] Philip also put the Aeagean coast as far east as Acontisma (not the banks of the Nestos river as often assumed) under direct Macedonian administration.

[73] After asking the Persian king Artaxerxes III to cut the support of the Ionian towns for Cersebleptes,[74] Philip finally felt confident enough to begin his most ambitious project so far: the conquest of inland Thrace in the form of a large campaign that would last from 342 to 340.

[71] The Getae, a northern Thracian people[76][77][78] located between the northeastern foothills of the Haemus range and the lower Danube and the Black Sea, had been part of the Odrysian realm since Teres I, even though it is not clear how tightly they were actually incorporated into the state.

[83] The conquest of the Odrysian kingdoms doubled the size of the domains ruled by Philip II,[89] even though inland Thrace was not transformed into a Macedonian province, but was put under the loose control of a Strategos.

Local Thracian rulers who seemed trustworthy were allowed to rule on Macedonian behalf, granted that they would pay a tithe and provide troops.

[95] The situation south of the Haemus remained largely stable for the next few years,[96] albeit even here, Macedon never managed to impose its rule over all Thracian tribes.

[105] In any case, both parties eventually reached a settlement, restricting Seuthes to the interior and Lysimachus to the coastal regions of the Aegean and Black Sea.

[103] The size and power of this kingdom should not be overestimated, as its influence was most likely limited to the hinterland of Seuthopolis,[113][114] in particular the valley between the Rhodopes in the south to the Haemus in the north and the Syrmus in the west to the upper Tonzos in the east.

[129] In the east was the kingdom of Tylis, a Celtic-dominated predator state which existence was based on blackmailing tribute and that was eventually destroyed by a Thracian revolt or attack[130] soon after 220.

[131] In the southeast and based at the town of Lysimachia, the Seleucids established themselves under Antiochus II (r. 261–246), who relied on allied Thracian dynasts to expand his influence deep into the interior.

[162] It can be assumed that, as in early Macedon, the Odrysian kings formed the heart of the realm and controlled the policy and the minting of coins, appointed loyal deputies and commanded the troops on the battlefield.

[167] This changed somewhat in the late 4th century, when Seuthes III founded Seuthopolis, marking the establishment of early state-like institutions[151] which were probably inspired by those of Hellenistic Macedon.

The infantry used bows, slings, spears, swords, axes and light crescent-shaped shields called pelte, giving these warriors their name: "peltasts".

[193] The list below includes the known Odrysian kings of Thrace, but much of it is conjectural, based on incomplete sources, and the varying interpretation of ongoing numismatic and archaeological discoveries.