▁during ▁the ▁anti - Christ ian ▁campaign ▁of ▁Had rian . ▁ ▁From ▁the ▁ 2 nd ▁to ▁the ▁ 4 th ▁centuries , ▁the ▁main ▁language ▁used ▁to ▁spread ▁the ▁Christian ▁religion ▁was ▁Latin , ▁whereas ▁in ▁the ▁ 4 th ▁to ▁the ▁ 5 th ▁centuries ▁it ▁was ▁Greek ▁in ▁Ep irus ▁and ▁Mac ed onia ▁and ▁Latin ▁in ▁Pra eval it ana ▁and ▁D ard ania . ▁Christian ity ▁spread ▁to ▁the ▁region ▁during ▁the ▁ 4 th ▁century . ▁The ▁following ▁centuries ▁saw ▁the ▁ere ction ▁of ▁characteristic ▁examples ▁of ▁By z antine ▁architecture ▁such ▁as ▁the ▁churches ▁in ▁Kos ine , ▁M bor je ▁and ▁Ap oll onia . ▁ ▁Christian ▁b ish ops ▁from ▁what ▁would ▁later ▁become ▁eastern ▁Alban ia ▁took ▁part ▁in ▁the ▁First ▁Council ▁of ▁N ica ea . ▁A rian ism ▁had ▁at ▁that ▁point ▁extended ▁to ▁Il ly ria , ▁where ▁Ari us ▁himself ▁had ▁been ▁ex iled ▁to ▁by ▁Const antine . ▁ ▁Middle ▁A ges ▁▁ ▁Since ▁the ▁early ▁ 4 th ▁century ▁AD , ▁Christian ity ▁had ▁become ▁the ▁established ▁religion ▁in ▁the ▁Roman ▁Empire , ▁supp lant ing ▁pag an ▁poly the ism ▁and ▁e cli ps ing ▁for ▁the ▁most ▁part ▁the ▁human istic ▁world ▁out look ▁and ▁institutions ▁inherited ▁from ▁the ▁Greek ▁and ▁Roman ▁civil izations . ▁E cc les iast ical ▁records ▁during ▁the ▁S lav ic ▁invas ions ▁are ▁sl im . ▁Though ▁the ▁country ▁was ▁in ▁the ▁fol d ▁of ▁By z ant