The location of the town was a good one, and in particular there was a pass there to the Labeatae, Gentius' kingdom. One of Perseus' men familiar with the area said there was no point in taking Oaeneum unless he controlled Draudacum. Perseus took Draudacum with ease. However, when Perseus reached Oaeneum, it could not be taken without a full-scale assault. Its strength lay in having rather more men of military age than other places, in the fortified walls of the town, and in being enclosed on one side be a river and on the other by a mountain which was very high and difficult of access. These factors gave the townspeople some hope of resisting. Perseus invested the town and began constructing a ramp on the upper side of the city; its height would bring him up over the city walls. As soon as the ramp reached the city wall, the assault began and led to Perseus capturing Oaeneum. The town was plundered and the adult males were slaughtered. By 168 BC, Gentius and Perseus were both defeated by the Romans and the area of Oaeneum became a part of the Roman province of Illyricum  Oaeneum remained with in Illyricum until Diocletian's reform and Oaeneum became a part of Epirus Nova in the 4th century AD. Due to the large barbaric incursions by the Celts, the Ostrogoths led by Theoderic the Great and the Huns from the 3rd century AD, the Romans started to build strong in-wall cities and fortresses on dominant hills around the area of Oaeneum. Christianity spread to Oaeneum during the later period of Roman invasion and reached the region relatively early. St Paul preached the Gospel in the region. In the 2nd to the 4th centuries, the main language to spread the Christian religion was Latin. However, after the Byzantine Empire was formed from the Roman Empire, Greek was the main language used. After the strong Avaric-Slavic incursions in the late 6th century AD, all the fortresses were abandoned but not entirely demolished. Before the middle of the 9th century, the region became part of the First Bulgarian Empire. The area came under Byzantine rule again in 1018. In the 13th and 14th centuries, Byzantine control was punctuated by periods of Bulgarian and Serbian rule. Konstantin Asen ruled as Tsar of the Bulgarian Empire from 1257 to 1277.