Martyrium of St. Philip - Hierapolis
Biblical Archaeology Review has published an extensive and informative article by Francesco D'Andria about the Martyrium of St. Philip in Hierapolis (Turkey) (July/August, 2011). According to the Acts of Philip, he was crucified upside down in Hierapolis after healing the wife of the proconsul. An octogonal monument was built around the site of his crucifixion and relics. A long and steep processional staircase leads to the Martyrium from the center of Hierapolis past a bath complex used for purification.
Hierapolis is a great archaeological site not far from Colossae and Laodicea. It is a good destination for groups seeking to contextualize early Christianity as Hierapolis was an important sanctuary of Apollo and Hades. It is an active geological site with earthquakes that open up fissures releasing underground gases - thus the focus on Hades. It was also a spa and healing center and includes an extensive necropolis. In addition to the Martyrium, there are a few additional Byzantine-era churches that have been excavated.
The Martyrium is a good example of how architecture includes religious symbols and messages. According to D'Andria, the octogonal form is symbolic of eternity, time without end. The seven side chapels are symbolic of the seven days of creation. The four triangular courtyards symbolize the four Gospels and their triangularity refers to the Trinity.