In the historic center of the city of Serres, the Church of Agios Theodoros stands as a reference point from the medieval years, operating to this day. Also known as the "Old Metropolis", as it functioned as a metropolitan church since Byzantine times, it is the most important surviving Byzantine monument of the city.
Historical reports characterize it as early Christian, placing its construction in the 5th or 6th century, while during the mid-Byzantine period it underwent successive repairs and reconstructions that continued until its partial destruction in 1913. In the 30s it was restored, saving significant mosaics which adorned its interior the one that depicts Apostle Andrew. The rhythm of the church is a large Rectangular Basilica, divided into three aisles by two rows of colonnades and inside the sanctuary presents all the elements of the Hellenistic Basilica.