The territory that is now Romania first appeared in history as Dacia. Most of its inhabitants were originally from the region of Thrace, in Greece; they were called Getae by the Greeks, and later, by the Romans, they were known as Dacians. Between ad 101 and 106 Dacia was conquered by Roman emperor Trajan and incorporated into the Roman Empire as a province. Roman colonists were sent into Dacia, and Rome developed the region considerably, building roads, bridges, and a great wall that stretched from what is today the Black Sea port of Constanŝa across the region of Dobruja to the Danube River.

In the middle part of the 3rd century the Goths drove the Romans out of much of Dacia. In about 270 Roman Emperor Lucius Domitius Aurelian decided to withdraw the Roman legions and colonies to an area south of the Danube; some Roman civilians chose to stay, however. Under the influence of the Romans, the people of Dacia adopted the Latin language.

For the next thousand years, the Daco-Roman people were subjected to successive invasions by the Huns, Avars, Slavs, and Bulgars. Slavs brought Christianity to the region in the 4th century, and through intermarriage and assimilation, changed the ethnic balance in Romania. Its inhabitants developed into a distinct ethnic group, known as the Vlachs, a name designating Latin-speakers of the Balkan Peninsula. In the 9th century the Eastern Orthodox form of Christianity was introduced by the Bulgars.

In 1003 King Stephen I of Hungary established control over most of the region of Transylvania in what is now central and northwestern Romania. In the 13th century King Béla IV of Hungary brought Saxons and other Germanic tribes into Transylvania to strengthen Hungary’s position there. In the middle of the 13th century Hungarian expansion drove many Vlachs to settle south and east of the Carpathian Mountains. There they established the principality of Walachia, and later that of Moldavia. Each was ruled by a succession of voivodes (native princes), who were generally under the authority of either Hungary or Poland. Until the 19th century the history of Romania was that of the separate principalities of Walachia and Moldavia.