TIMELINE OF CONFLICTS
Emperor Trajan himself wrote a memoir of his campaigns in Dacia, though that work has not survived to this day. Cassius Deo gave a few pages to the in his Histories, 67-68 Here is a brief overview
85AD The Dacian king Decebalus begins raids in the Roman province of Moesia (south of the River Danube).
86AD Roman Emperor Domitian sends his prefect of the Praetorian Guards, Cornelius Fuscus, to retaliate. It ends in disaster for the Romans. Two Legions are destroyed.
88AD Tettius Julianus leads a new attack on Dacia. The battle of Tapae is an important win for the Romans. As the Dacians near total defeat, the Romans make a hasty treaty and pull out to quell of the revolt of the Roman general, Antonius Saturnius, on the Rhine. There was also trouble with the German tribes in that area. According to Cassius Deo, the treaty was extremely embarrassing for the Romans. They had to pay the Dacia large sums of money, and they had to send captives of artisans and military craftsmen. Domitian strengthens the defenses on the Roman side of the river and divides the Province of Moesia into two: Lower and Upper.
96AD The unpopular Domitian is murdered. Nerva takes his place and adopts Trajan as his heir.
98AD Trajan is made emperor at Nerva's death.
101AD Drawn by its vast supplies of gold or revenge, Trajan prepares for a new war with Dacia. He raises 2 new legions (XXX Ulpia and II Tajana) to replace the ones Cornelius Fuscus lost in 86AD. 13 legions were made available to invade Dacia. Trajan moved in tot he country meeting little resistance. As winter sets in the Romans fortify what they have conquered and set up camp. Decebalus leads a sneak winter attack into Lower Moesia. It's repulsed.
102AD Trajan headed toward the Dacian capitol, Sarmizegetua, laying siege to Dacian fortresses on the way. When he finally reaches the capitol, Decebalus sues for peace. He is allowed to remain King under Roman direction. Trajan leaves some troops behind and returns to Rome with the title "Germanicus."
105AD After secretly rebuilding his forces, Decebalus wipes out the Roman garrisons in Dacia. Trajan returns and defeats the Dacians again. Decebalus tries to flee into the mountains, but he tracked down by Roman cavalry and commits suicide before he can be captured. Sometime after 106AD Dacia is made a Roman province, however there remained a section of Dacia to the mountainous north never occupied by Rome.
References:1. Dio Cassius. Roman History. Volume VIII, Books 61-70.
2. Peter Wilcox. Rome's Enemies (1): Germanics and Dacians
3. Peter Connolly. The Legionary
4. Peter Connolly.The Cavalryman