The Roman province Dacia Traiana, established by the victors of the Dacian Wars during AD 101–106, initially comprised only the regions known today as Banat, Oltenia, Transylvania, and was subsequently gradually extended to southern parts of Moldavia, while Dobruja and Budjak belonged the Roman province of Moesia.
In the 2nd century AD, after the Roman conquest, Ptolemy puts the eastern boundary of Dacia Traiana (the Roman province) as far east as the Hierasus (Siret) river, in the middle of modern Romania.
The Greeks referred to them as the Getae (east of Dacia) and the Romans as Daci.
Dacia was bounded in the south approximately by the Danubius river (Danube), in Greek sources the Istros, or at its greatest extent, by the Haemus Mons.
Moesia (Dobruja), a region south-east of the Danube, was a core area where the Getae lived and interacted with the Ancient Greeks.
In the east it was bounded by the Pontus Euxinus (Black Sea) and the river Danastris (Dniester), in Greek sources the Tyras.
A Dacian Kingdom of variable size existed between 82 BC until the Roman conquest in AD 106.
The capital of Dacia, Sarmizegetusa, located in modern Romania, was destroyed by the Romans, but its name was added to that of the new city (Ulpia Traiana Sarmizegetusa) built by the latter to serve as the capital of the Roman province of Dacia.
After the Marcomannic Wars (AD 166–180), Dacian groups from outside Roman Dacia had been set in motion.″As for the southern part of Germany beyond the Albis, the portion which is just contiguous to that river is occupied by the Suevi; then immediately adjoining this is the land of the Getae, which, though narrow at first, stretching as it does along the Ister on its southern side and on the opposite side along the mountain-side of the Hercynian Forest (for the land of the Getae also embraces a part of the mountains), afterwards broadens out towards the north as far as the Tyregetae; but I cannot tell the precise boundaries″ On this basis, Lengyel and Radan (1980), Hoddinott (1981) and Mountain (1998) consider that the Geto-Dacians inhabited both sides of the Tisza river prior to the rise of the Celtic Boii, and again after the latter were defeated by the Dacians.In the 1st century AD, the Iazyges settled West of Dacia, on the plain between the Danube and the Tisa rivers, according to the scholars' interpretation of Pliny's text: "The higher parts between the Danube and the Hercynian Forest (Black Forest) as far as the winter quarters of Pannonia at Carnutum and the plains and level country of the German frontiers there are occupied by the Sarmatian Iazyges, while the Dacians whom they have driven out hold the mountains and forests as far as the river Theiss".The Dacians are first mentioned in the writings of the Ancient Greeks, in Herodotus (Histories Book IV XCIII: "[Getae] the noblest as well as the most just of all the Thracian tribes") and Thucydides (Peloponnesian Wars, Book II: "[Getae] border on the Scythians and are armed in the same manner, being all mounted archers").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.