Ancient Dacia was located north of Macedon and Greece on the eastern side of the Danube river.   The Dacians were always considered a threat to the Roman empire because of their location on the border of some of the furthest provinces of the Empire.  Rome fought several wars against the Dacians, the first from 86-88 AD under Emperor Domitian after the Dacian Army of King Duras attacked the Roman Province of Moesia in 86 AD, killing the Roman governor.  After initial Roman defeats, the Romans continued their offensive and eventually a truce was agreed too by Domitian in 88 AD due to more pressing military matters elsewhere.   The more famous wars with the Dacians were Emperor Trajans two wars, the first between 101-102 AD and the second from 105-106 AD.   In the first war, Roman military power and engineering carried the day and the now Dacian King Decebalus requested peace.   However, he continously violated the terms of the peace and Trajan again advanced his legions.   The Dacian wars were costly to Rome's military, but eventually Dacia was subjugated and it was a great triumph for Emperor Trajan.  The conclusion of these wars marked the start of a period of sustained growth and peace for the Roman Empire.