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. Middle Ages 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. Later the region was overrun and taken by Serbian Tsar Stefan Dušan. Between the years 1348-1353, Albanians are mentioned by Serbian Tsar Stefan Dušan as farmers and soldiers in the district of Tetovo. In 1337, Dušan restored the Monastery of St Mary (Lešok Monastery) and gifted the monastery the Albanian villages, as well as the Nanov Dol highlands. Dušan barred everyone, the Albanians included, from grazing the sheep in these highlands. After the dissolution of the Serbian Empire, the Mrnjavčević house took the region. This did not last as the Ottomans made their way to the region. The initial Ottoman occupation did not last as Skanderbeg and his Albanian force with aid from Tetovo, took on the Ottoman forces led by Ibrahim Pasha in the Battle of Pollog. Skanderbeg slayed Ibrahim Pasha, who was an old friend of his during his time with the Ottomans. Tetovo came under Albanian control. In August 1462, After Skanderbeg defeated Ottoman forces under Hasan bey in Mokra, Isuf bey went to move against Skanderbeg. Isuf bey marched out with 18,000 troops to Uskub. From there, he marched onto Pollog near Tetovo. Skanderbeg attacked and annihilated Isuf's force and the Pasha fled, leaving his army behind to be