The Church of St. John Promodos was a church located at the Hebdomon, a coastal Constantinopolitan suburb on the Via Egnatia seven miles west of the Milion. It was first built by Theodosius I to house the relic of the head of St. John the Baptist and later rebuilt during the reign of Justinian. It was an important monument of the Hebdomon (modern Bakirköy), where several emperors were crowed. It is also known that this church was rebuilt or more likely restored by Basil I.

The remains of an octagonal church, generally identified as St. John Prodomos, were uncovered at Bakirköy by French excavations in 1921-1923. Only a few pier foundations and part of the apse were discovered. However the remains of the building, along with a description of the church by Procopius, allow for a partial reconstruction of the church. This church (or martyrion) had an octagonal plan similar to the churches of San Vital in Ravenna and Sergius and Bacchus in Constantinople. It consisted of a octagonal nave surrounded by an octagonal ambulatory and galleries. The last traces of the church disappeared in 1965 with construction of the Bakırköy Hospital. Several architectural remains are now on display at the Istanbul Archaeological Museums.