Church of Saint Jacob of Nisibis

Mar Yakov Church or Mor Yakup Church, also known as the Church of Saint Jacob in Nisibis, is a historic church in Nusaybin, southeastern Turkey. Archaeological excavations revealed that the 4th-century church building was originally the baptistery of a cathedral, which no longer exists. It is not determined whether this church belonged to Syriac Orthodox Church or the Church of the East, but it is under the jurisdiction of the Syriac Orthodox Church which it is most likely linked to.

Source: Wikipedia