Philadelphia

To the angel of the church in Philadelphia, write this:
The Holy One, the True One, who holds the key of David, who opens and no one will shut, who shuts and no one will open, says this: "I know your deeds (look, I have placed before you an open door that no one can shut). You have little strength, yet you have kept my word and have not denied my name. Look, I will make those of the synagogue of Satan, who say they are Jews but are not, but lie, behold, I will make them come and bow down before your feet, and they will know that I love you.
Because you have kept my command to endure patiently, I will also keep you from the hour of trial that is coming to the whole world to test those who dwell on the earth. I am coming soon. Hold on to what you have, so that no one will take your crown.
The one who is victorious will be made a pillar in the temple of my God. Never again will they leave it. I will write on them the name of my God and the name of the city of my God, the new Jerusalem, which is coming down out of heaven from my God, and I will also write on them my new name."
"Whoever has ears, let them hear what the Spirit says to the churches."
(Revelation 3:7-13)

The church in Philadelphia, located at an important crossroads of the imperial post road, had a unique opportunity to spread the gospel through the open door before them. Despite this, they faced opposition from a synagogue of Satan, although archaeological evidence for a synagogue has not been found. However, a 3rd-century A.D. inscription found 10 miles east of the city mentions a "synagogue of the Hebrews."
Philadelphia, like Sardis, was located in an earthquake-prone area known as Catacecaumene. Both cities were devastated by earthquakes in A.D. 17. In response to these frequent earthquakes, Asian temples were built with special foundations to endure tremors. These foundations, laid on beds of charcoal covered with wool, allowed the structures to "float" like rafts. The walls of the temples were connected by metal cramps, making them secure and united.
This construction style made the temple the most durable building in the city, which is why the promise of being made a pillar in the temple of God symbolizes security and stability. Inscribed pillars were common throughout Aegean Turkey, such as the dramatic example of the temple of Zeus at Euromos, where ten of the eleven standing pillars were inscribed with dedicatory inscriptions.
Philadelphia also underwent two name changes in the first century: first to "Neocaesarea" after the A.D. 17 earthquake in recognition of Tiberius' generosity, and later to "Flavia" following financial support from Vespasian after another catastrophe.