The Dacians are the subject of Trajan's Column - Dacia was a kingdom equating to Romania & Moldova, & also parts of Serbia, Bulgaria, Hungary, Poland & Slovakia. This image shows two Dacian warriors on the Arch of Constantine. 
The Dacian kingdom under their last king, Decebalus, covered around 400,000 square kilometres. This powerful kingdom was seen as a threat to Rome & Decabalus had mounted successful raids south of the Danube. The images show Dacians on Trajan's Column.
The Roman Emperor, Domitian, tried to deal with the Dacian threat with disastrous campaigns in AD86 & 88. Domitian had to settle diplomatically with Dacia. The Emperor Trajan decided to try & conquer Dacia launching two wars (The Dacian Wars) in AD101-102 & AD105-6.
At the end of the 1st War, Decabalus sued for peace on terms favourable to the Romans, but this was seen as temporary & in AD105, Trajan besieged the Dacian Capital, Sarmizegetusa. The siege eventually succeeded & Decabalus fled, committing suicide as shown on Trajan's Column
Around half the kingdom of Dacia was assimilated into the Roman Empire, with the reminder remaining outside the Empire. Trajan's column was constructed to celebrate the triumph of the Empire over the Dacians.
