What is the Decapolis?:
The Decapolis was a federation of ten hellenized cities. This league was originally the creation of Alexander the Great and his successors. According to Pliny the Elder, the cities of the Decapolis included Canatha, Gerasa, Gadara, Hippos, Dion, Pella, Raphaana, Scythopolis, and Damascus. Of these, four were most important: Gadara, Pella, Abila, and Scythopolis.
Where is the Decapolis?:
The cities of the Decapolis were located in Galilee and eastern Samaria, primarily along the eastern edge of the Sea of Galilee and the Jordan river. By Plinys time, the label Decaoplis referring both to the cities themselves and the region they were located. Today this region is within the Kingdom of Jordan and the Golan Heights.
Why is the Decapolis important?:
The cities of the Decaopolis help demonstrate the importance of urbanization for the spread of Greek civilization as well as the role cities had for Romes ability to control a region. It was here that Greco-Roman culture was first imported and it was from cites like this that it spread: theaters, schools, philosophy, etc. These cities were also quick to side with Roman authorities whenever the rural populations rose up in revolt.
These were very cosmopolitan cities, bringing Romans, Greeks, and others into close, extended contact with indigenous peoples. Archaeological excavations find pagan temples almost side-by-side with Jewish synagogues and Christian churches.
The Decaoplis is mentioned a couple of times in the gospels in reference to Jesus activities. First a man he heals goes there to report on Jesus ability, and later Jesus himself travels to the region to perform more healings:
And when he was come into the ship, he that had been possessed with the devil prayed him that he might be with him. Howbeit Jesus suffered him not, but saith unto him, Go home to thy friends, and tell them how great things the Lord hath done for thee, and hath had compassion on thee. And he departed, and began to publish in Decapolis how great things Jesus had done for him: and all men did marvel. (Mark 18-20)
And again, departing from the coasts of Tyre and Sidon, he came unto the sea of Galilee, through the midst of the coasts of Decapolis. And they bring unto him one that was deaf, and had an impediment in his speech; and they beseech him to put his hand upon him. And he took him aside from the multitude, and put his fingers into his ears, and he spit, and touched his tongue; And looking up to heaven, he sighed, and saith unto him, Ephphatha, that is, Be opened. (Mark 7:31-34)