Domitian was drawn into a war against the Dacians, who inhabited the area of modern day Romania. The Dacians who had been in Rome’s cross-hairs since the time of Caesar had crossed into the Roman province of Moesia and killed the Moesian governor Oppius Sabinus.
The Dacian crossing of the Danube under their new King Decebalus was an audacious move bound to attract a Roman response and leaving the Emperor Domitian very little choice but to respond with military force. Even Suetonius who accuses the emperor of engaging in unprovoked campaigns readily admits that this was not one of them.The Dacian raid took the Roman garrison in Moesia by complete surprise
Sabinus marched against the invaders with the 5th Macedonica legion which was based at Oescus. Sabinus suffered a severe defeat at Decebalus’ hands and was himself was killed in the winter of A.D. 85 the 5th Macedonica was heavily mauled and forced to fall back. The 4th Flavia legion and auxiliaries were rushed from Dalmatia to Moesia but by the time they arrived Decebalus had already sacked several cities and towns and had taken many prisoners.
Domitian accompanied by Cornelius Fuscus the praetorian prefect marched to Moesia and set up a base at Naissus. Dio tells us that Domitian in Moesia was busy drinking and engaging lewd behaviour with women and boys alike. The fact that Domitian accompanied the Roman forces as far as Moesia demonstrates that at the very least he wished to be associated with a victory against the Dacians if the descriptions of his conduct whilst in the region are purely the result of an anti-Domitianic tradition that is clearly visible in the sources the chances are that although not on the front himself he was orchestrating events from a rearguard position.
Apparently Decebalus sent several envoys to the Emperor Domitian requesting a truce so that Rome and Dacia could return to peaceful terms, Domitian repeatedly rejected these overtures as accepting these would certainly have made the Emperor and Rome look weak in the eyes of the Dacians and their neighbours after the nation raid into Roman territory and the killing of a Roman official a military response was essential.
Cornelius Fuscus who was sent against the Dacians with a large force some time in the year A.D.85. Fuscus at the head of the five legions initially met with some success in his campaign against the Dacians and was able to expel them from Moesia.
But the Dacian forces were not to be that easily defeated as Decebalus was an extremely intelligent commander and King himself led the Dacians forces against Domitian’s Roman forces.
Cornelius Fuscus, who was not renowned for his patience, crossed the Danube in pursuit of the Dacians to avenge the death of Oppius Sabinus and win more glory for Rome. The Roman commander crossed the Danube by means of the bridge of boats, it appears that the Roman advance into Dacia was largely uncontested and that the low land regions had been abandoned by the Dacian military in favour of their fortresses located in the mountains.
The suggestion made by Dio that Decebalus had a very solid understanding of warfare and was an expert in ambushes as well as pitched battles is clearly demonstrated by the tactics he chose to employ against the Roman forces. The site of the engagement with the forces of Cornelius Fuscus was located in the Orastie mountains possibly near Tapae.
Tapae was located somewhere near the iron gate pass. The iron gate pass was a 15km long narrow passage which formed a formidable obstacle in its natural state made more so by the Dacian addition earthen defence works.
Unfortunately for the Romans Decebalus having drawn the Roman forces into terrain more suited to the Dacians was well-prepared and executed an ambush against Fuscus and his forces, the ambush worked exceptionally well and the Roman commander and Legio V Alaudae were all killed. The Dacians captured the Roman standards, the Roman war machines and Jordanes tells us that they plundered the soldiers’ camp of all its wealth.
Tettius Julianus was appointed Governor of upper Moesia replacing Vettonianus. Julianus had been consul in AD 83 and had demonstrable experience on the Danube. He had commanded the 7th Claudia legion where he defeated the Roxolani in A.D. 69.
Julianus had a reputation as a stern disciplinarian, which was exactly what was needed after the impetuous nature of Fuscus which led to a significant Roman defeat. Domitian’s second attack against Dacia occurred in the year A.D. 88 under the command of the new Governor of upper Moesia.
The Roman forces first went to Viminacium across the Banat to the Iron Gates in an effort to reach the Dacian capital of Sarmizegetusa Regia and the Dacian King Decebalus. However in late A.D. 88 the second attack against the Dacians concluded with a battle at Tapae, where the Romans defeated the Dacian forces but before the Romans were able to reach the Dacian capital.
Domitian was pushed into coming to terms with Decebalus to minimise the possibility the Rome would be engaged in a war on two fronts.
The treaty struck with the Dacians and Decebalus which has been roundly criticised by the ancient sources and many modern sources included a large financial payment to Decebalus and continuing financial stipends paid annually, the supply of Roman technical experts, and Decebalus was made a client King of Rome most likely with the intention of using Dacia as a buffer zone between the Roman provinces located South of the Danube and the Peoples North of the Danube. Rather than going to Rome himself Decebalus sent a member of the royal family Diegis to Rome to accept the Crown from Domitian rather than turning up himself a further insult to Rome which was probably a very wise idea considering how the Romans probably felt about him.