Revelation 2-3: Monarchical Bishops By 95 AD
It's been argued that Jesus Himself, cited by St. John in the book of Revelation (written around 95 AD), taught monepiscopacy (the notion of one bishop I examine what can be historically determined about the seven churches of Revelation 1-3 (around 95 AD), whose "angels" have been interpreted to be bishops.
Source: patheos.com