Burebista is widely considered to be the greatest king of Dacia. He ruled between 82 BC and 44 BC. He unified the Thracian population from Hercynia (today's Moravia) in the west, to the Bug River in the east, and from the northern Carpathians to Dionysopolis. His capital was called Argedava (or Sargedava).

The spiritual center of the kingdom was called Kogaion (or Kagaion, the holy mountain) by the ancient geographer Strabo. It is believed to have been located somewhere in the Bucegi mountains. According to the historian Jordanes (in his work Getica), the greatest priest and adviser of Burebista was Deceneus, who held "almost royal powers" and taught the Dacians the belagines laws, ethics and sciences, including physics and astronomy.

Around the year 70 B.C., external conditions being propitious and Burebista's political and military actions successful, the Geto-Dacian people had a unique and firm rule, and a strong organization. Under Burebista, who thoroughly reorganized the army and raised the moral standard of the people, the limits of the kingdom were extended to their maximum. The Bastarnae and Boii were conquered, and even the Greek towns of Olbia and Apollonia on the Black Sea (Pontus Euxinus) recognized Burebista's authority. Burebista sided with the inhabitants of the Greek cities on the Western coast of the Black Sea from Apollonia to the Danube Delta (South of the Danube) when they were occupied by Varro Lucullus, the proconsul of the province of Macedonia during the second Mithridatic War (74 BC-72 BC). The Dacians defeated the Roman army of Gaius Antonius Hybrida near Histria. As a result of this battle, the Greek cities of Tomis, Callatis, Dionysopolis and Apollonia agreed to become part of Burebista's kingdom.

Burebista continued his incursion in the region, conquering the Celtic Aliobrix (Cartal, southern Bessarabia, now part of Ukraine), Tyras and Odessos and destroying Olvia (Olbia). In this way, Burebista came to rule over the whole Thracian-Geto-Dacian world, from the Haemus Mountains (the Balkans) to the Wooded Carpathians, from Tyras (the Dnestr) to the Tisza. Controlling both sides of the Danube, Burebista was "the first and the greatest of the Thracian kings", as he is referred to in writing by Acornion of Dyonisopolis. The unifying centre of the Geto-Dacian state lay in the Orăştie area (Sureanu Mountains) - a natural Transylvanian stronghold; there, Burebista developed a whole system of fortifications, which was to be continued by his followers Dicomes, Scoryllo, Cotiso.

His successful unifying endeavour, which led to the unity of the Geto-Dacian people, language and civilisation, made the king feel stronger, a fact which led him into believing that he was capable of measuring his military strength with that of the Romans. In 48 BC, Burebista sided with Pompey during his struggle against Julius Caesar in the Roman civil war. After Caesar emerged as victor, he planned on sending legions to punish Burebista, but he was assassinated in the Senate before he could do so, on March 15 44 BC. Burebista died the same year, but whether he was assassinated in a court plot or his death had natural causes is a matter that remains uncertain. After his fall, the state weakened and lost part of its territory, the kingdom was divided into four (or five) parts under separate rulers. One of these was Cotiso, whose daughter Augustus is said to have desired to marry and to whom Augustus betrothed his own five-year-old daughter Julia. He is well known from the line in Horace (Occidit Daci Cotisonis agmen).