In the Book of Revelation, the angel sent to John the Evangelist tells him (Revelation 1:11, KJV):

What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea.

These were seven of the early Christian churches in Asia Minor.