These complex societies have been studied extensively by the Romanian Institute of Thracology, an interdisciplinary school of anthropology, archaeology, ethnoarchaeology, ethnology, ethnomusicology, and linguistics that publishes the journal Thraco-Dacia. In the beginning of the Hallstatt period in western Romania, the Gava, Susani, and Insula Banului cultures thrived, making black pottery. The Insula Banului spread east along the Danube River, contributing to the formation of the Babadag culture in Dobroudja and the Cozia-Brad culture in Moldavia, characterized by imprinted pottery. These communities practiced agriculture and bred cattle; some had burial rites of inhumation (supine corpses) and others cremation; their necropolises were either flat or tumuli. Later, in Moldavia and Transylvania, came the Mediaş and Reci cultures. In the middle Hallstatt, the Basarabi culture covered a great expanse of territory in southwestern Romania; it was identified with bitronconic vessels, jars, and dishes, all with spiral ornaments. Simultaneously, the Babadag culture continued to develop in Dobroudja, with settlements of earthen huts protected by ditches and walls, and with black and incised white encrusted pottery.

In the late Hallstatt period, the local population flourished under the influence of the southern Thracians. In Moldavia, fortress-like settlements point to the existence of some well-organized tribes of Thracians known as Gets or Dacians, depending on the archaeological source. Greek colonies on the Black Sea coast also played an important role in the development of Thracian culture. Histria was founded in 657 b.c. and issued silver and bronze coins beginning around the middle of the fifth century b.c.; arrowheads were sometimes used as currency in neighboring areas. The Thracian culture occupied the hilly southern area of Bârseşti-Ferigile, with tumuli cremation burial sites that contained some Scythian weapons (akinakes, axes, and rare vessels made on pottery wheels). Nomadic Scythians had invaded from the north Pontic steppes. They spread to Moldavia and along the Danube plain and also from the west into Transylvania, where the Agathirsies culture has been documented (Vasiliev 1980). However, outside the Carpathian region, their forays are believed to have been only temporary.

In all Romanian provinces, archaeologists have discovered complexes dating to the late Iron Age, or la tène, period (Berciu 1967; Daicoviciu, C. 1945; Daicoviciu, H. 1965; Părvan 1926). The Geto-Dacians, who built these settlements, were direct ancestors of the present-day Romanian people. The Geto-Dacians experienced several other invasions. As early as the first half of the fourth century b.c., Celtic communities invaded from the west (Crişan 1971, 149–164; Zirra 1971, 171–238). At the same time, western Oltenia and part of Banat came under the rule of Scordisci Celts. The Gets, under the leadership of Dromichaites, defeated the Macedonian army led by Lisimach, who was taken prisoner. At the end of the third century b.c., the Bastarns, a Germanic people, penetrated Moldavia from the north, creating the Poieneşti-Lukaşevka culture. Celtic rule lasted in the area until the end of the second century b.c. However, by the first century b.c., the Geto-Dacians had achieved superior tribal organization in the south, with fortresses (dava) and military chieftains, and by the middle of the first century, they had established a center in southwestern Transylvania under King Burebista. During that period, the Geto-Dacians conquered a wider territory and Dacia extended from the Middle Danube to the Black Sea littoral (between Apollonia and Olbia) and from present-day Slovakia’s mountains to the Balkan mountains.

The Geto-Dacians maintained two social classes: tarabostes (aristocrats) and comati (common people). An aristocratic “council” and great priest helped the king rule the population. The Geto-Dacians practiced various occupations; predominantly agriculture on the plains and cattle breeding in the foothills and mountains. Hunting, fishing, pottery making, metallurgy (iron, silver), salt extraction and processing, viticulture, arboriculture, and beekeeping were also known (Vulpe 1976, 19–21). The Geto-Dacians used diverse tools (plows, scythes, sickles, axes) and weapons (swords, spears, knives, lances) made of iron. Many settlements were built on