Campestris is located in the area of modern Mopsuestia in Anatolia, 20 km east of Antiochia ad Cragum. Its foundations are said to lie in the legend of the soothsayer Mopsus who lived there before the Trojan War. Pliny the Elder mentions the city as Mopsos in 5.22. It was mentioned also by Stephanus of Byzantium and the Christian geographers. In the Seleucid Period it took the name 'Seleucia on the Pyramus' and then in the Roman conquest it was named under Hadrian as 'Hadriana' and later under Decius as 'Decia'.
Its main historical claim to fame lies in the Byzantine Period when Constantius II built a magnificent bridge over the Pyramus which was later restored by Justinian as told by Procopius. Christianity was introduced to the city in the third century CE and its association with Christianity continued until it was taken over by the Arabs and became Islam. Forts were also constructed in this period. Efforts were made by the Byzantines to re-Christianise the city in the eleventh century.