Christianity soon spread over the Eastern Mediterranean after its first appearance in Palastine. A particular group of towns played an important role in that period of time such as Antiochia which used to be an important center since its foundation; Tarsus, the hometown of many philosophers and Seleucia ad Calycadnum with its important geographical location. St. Paul and St. Thecla played major roles in the spread of Christianity over Cilicia and Isauria. St. Paul’more tolerable approach towards Jewish – Christian belief is supposed to be a reason of this rapid acceptance of this new belief especially among Pagans. At such an important pagan center like Seleucia which had a Temple of Jupiter and its priests, St. Thecla spent a considerable effort for the spread of Christianity in the region. After the spread of Christianity in Isauria, Seleucia which was the capital of the Roman province became the seat of arcbishop of the region. The bishops of the smaller neighbouring towns like Diocaesarea and Olba were in direct contact with Seleucia ad Calycadnum. In the Eastern Mediterranean towns which had a rich cultural background and an ancesteral heritage, the discussions concerning with the nature of Jesus Christ soon became an aspect of discussion. Seleucia was presented in the all council meetings held on this matter. The names of the bishops of Seleucia ad Calycadnum who attended these council meetings were recorded in the Early Christian documents. St. Thecla’s life and her acts, the monastery and the church built for her, the town’s being the seat of arcbishop in Early Christian era and its presentation in the major council meetings reveal its significance as an important center of Christianity in the Early Byzantine period.