On the slope behind the theatre are vestiges of the Martyrium of Saint Philippe. This martyrium measuring 20 m by 20 m was constructed outside the walls in the name of this saint where he was martyrized. It is octogonal on a square ground-plan and stairs lead there from the city. Before the advent of Christianity the autochtones were Jews. Hierapolis is one of the biblical cities. There is a reference to it in the epistle of St Paul addressed to Colossaili. It follows that in that Epaphra of Colossaili was very active amongst the Christians of Laodicea and Hierapolis.
The martyrium was built at the end of IVth century of beginning of Vth. According to the opinion of Prof. Verzone, director of the excavations, in view of the perfection of the architecture it must have been made by an architect from the royal school of architecture. The four sides of Martyrium resembling a doublecross are surrounded by chambers. There are eight chapels separated from each other with polygonal spaces. From the chambers around the edifice one had access to the octogonal space covered at the time by arches. On both sides were porticoes used as shelters. The octogonal chamber in the middle was paved with marble. The entrance chambers were paved with limestone. The floor of other chambers were just earth.