Slavic tribes settled in the Balkan region including North Macedonia by the late 6th century AD. During the 580s, Byzantine literature attests to the Slavs raiding Byzantine territories in the region of Macedonia, later aided by Bulgars. Historical records document that in  a group of Bulgars, Slavs and Byzantines led by a Bulgar called Kuber settled in the region of the Keramisian plain, centred on the city of Bitola, forming a second route for the Bulgar definitive settlement on the Balkan Peninsula at the end of the 7th century. Presian's reign apparently coincides with the extension of Bulgarian control over the Slavic tribes in and around Macedonia. The Slavic tribes that settled in the region of Macedonia converted to Christianity around the 9th century during the reign of Tsar Boris I of Bulgaria. The Ohrid Literary School became one of the two major cultural centres of the First Bulgarian Empire, along with the Preslav Literary School. Established in Ohrid in 886 by Saint Clement of Ohrid on the order of Boris I, the Ohrid Literary School was involved in the spreading of the Cyrillic script.