The Dacian Wars (101–102, 105–106) were two military campaigns fought between the Roman Empire and Dacia during Roman Emperor Trajan‘s rule. The conflicts were triggered by the constant Dacian threat on the Danubian Roman Province of Moesia and also by the increasing need for resources of the economy of the Roman Empire.
Trajan turned his attention to Dacia, an area north of Macedon and Greece and east of the Danube that had been on the Roman agenda since before the days of Caesar:213 when they defeated a Roman army at the Battle of Histria.:215 In AD 85, the Dacians swarmed over the Danube and pillaged Moesia(p216)(p53) and initially defeated the army that Emperor Domitian sent against them.:217 The Romans were defeated in the Battle of Tapae in 88 and a truce was established.:217
Emperor Trajan recommenced hostilities against Dacia and, following an uncertain number of battles,:219 defeated the Dacian King Decebalus in the Second Battle of Tapae in 101.:54 With Trajan’s troops pressing towards the Dacian capital Sarmizegetusa Regia, Decebalus once more sought terms.:329 Decebalus rebuilt his power over the following years and attacked Roman garrisons again in 105. In response Trajan again marched into Dacia,:222 besieging the Dacian capital in the Siege of Sarmizegetusa, and razing it.:223 With Dacia quelled, Trajan subsequently invaded the Parthian empire to the east, his conquests expanding the Roman Empire to its greatest extent. Rome’s borders in the east were indirectly governed through a system of client states for some time, leading to less direct campaigning than in the west in this period.:39