Founding
Ephesus is one of the 12 ancient cities of Ionia, that  date back to mythic times. According to legend it was founded when Hercules gave permission to the Amazons to settle there and build a city. If this is true it would put the cities founding somewhere in the hundred years after the patriarch Abraham died. Which would be about 500 years after the flood of Noah. See Greek Gods.

Goddess Dianna
The Temple of the Goddess Dianna, or Artemis, was located in the city of Ephesus and was one of the seven wonders of the ancient world. It was a massive temple (425 × 220 feet) with 127 60-foot marble columns. It was built out of cedar, cypress, white marble and gold. The temple was erected about 500 BC. Her worship was supposed to have started at Ephesus when a great object fell from heaven in very ancient times. At times her worship included human sacrifice and her worship was conducted by eunuch priests, called megabyzoi.

An ancient Statue of Dianna was found and is now in the Naples museum. It has a circle around her head with four griffins on each side of her head. In her breasts are the 12 signs of the zodiac. In front are the Ram, Bull, Twins, and Crab. She wears a necklace of acorns and has lions on her sleeves On the rest of her body are various beasts and monsters, like sirens, griffins, sphinxes. The statue is made out of brass with her head and hands out of alabaster.

The Apostle Paul
The Apostle Paul founded the church there and placed Timothy there as pastor. In acts 19:23-41 the gospel is already spreading so fast that the Idol makers are loosing prophet. So one would think the few worshipers of Dianna left in John's time would not pose too much of a problem. In Acts 19:17-20 the converts burned a large about of their magic scrolls. These were book and amulets and talismans for success and against despise namely from the goddess Dianna.

Under Roman rule Ephesus became the capital of not only Ionia but of all of Asia. It had the title of "The first and greatest metropolis of Asia." So it is logical that the headquarters of Christianity would move from Jerusalem to Ephesus. The bishop of Ephesus in later times was president of the Asiatic dioceses with all the rights and privileges of a Patriarch.

The Apostle John
The Apostle John was banished to the Isle of Patmos for being a Christian, while there he wrote the book of Revelation, in 96 AD. When roman emperor Domitian (81-96AD) died he decrees were nullified and John was released. John went back to the Asian capital Ephesus and set it up a headquarters for missionary activity. John lived there many years. John and his disciple Polycarp worked in sending out missionaries and planting churches for over 20 years. John died there of old age during the time of emperor Trajan. (98-117AD) Greek Tradition is that under the mosque are the remains of the church that was dedicated to St. John. Contained in it is the tomb of St. John and close by are the tombs of Timothy and Mary, the mother of our Lord.
John's gospel and epistles may have been written there.

Ephesus in Revelation 2
The church at Ephesus was great at rooting out and exposing the false apostles. Under John's control the Asian capital was able to expose all the Gnostic cults, including Cerinthus, John's ach enemy, the Nicolaitans, the Carpocrates, Ebionites, and others. By this time Simon Magus and his successor, Menander, were dead, but their cult were still surviving.
But the Church had lost its first Love. It was given the warning that unless it repents it will be removed.
The great Christian capitol was taken over by the Muslim Turks in 1308, the great church was replaced with Islamic mosque, and within a few decades Ephesus was laid to ruin and is no more.

Information taken from:
Cyclopedia of Biblical, Theological, and Ecclesiastical Literature; by Baker.
Early church Fathers; Eerdmans Pub.