Did The Early Church Teach Millenarianism?

A Thousand Years is Like a Day to God

Some believe that since God made/recreated the world in six days and rested on the seventh day (Genesis 2:1-3), that humans will have 6000 years to live on the earth under Satan's influence, but will have a 1000 years to be under Christ's reign (the original creation of the universe may have been billions of years earlier c.f. Genesis 1:2; Isaiah 45:18).

Many have noted that a thousand years seems to be as one day to God. This is a concept from both the Old and New Testaments:

For a thousand years in Your sight Are like yesterday when it is past (Psalm 90:4).

But, beloved, do not forget this one thing, that with the Lord one day is as a thousand years, and a thousand years as one day (2 Peter 3:8).

More information on the 6,000 year plan can be found in the article Does God Have a 6,000 Year Plan?

The Book of Revelation Teaches a Thousand Year Reign of Christ

Notice that the Book of Revelation makes it clear that God's people will reign on the earth with Christ:

9..."You are worthy to take the scroll, And to open its seals; For You were slain, And have redeemed us to God by Your blood Out of every tribe and tongue and people and nation, 10 And have made us kings and priests to our God; And we shall reign on the earth" (Revelation 5:9-10).

Thus, a future physical reign on the earth is clearly prophesied.

Notice that the Apostle Paul told Timothy that the true saints would reign with Jesus:

11 This is a faithful saying:
For if we died with Him,
We shall also live with Him.
12 If we endure,
We shall also reign with Him (2 Timothy 2:11-12).

Chapter 20 of the Book of Revelation clearly teaches, as it mentions it five times, that there will be a thousand year reign of Christ on the earth:

Then I saw an angel coming down from heaven, having the key to the bottomless pit and a great chain in his hand. He laid hold of the dragon, that serpent of old, who is the Devil and Satan, and bound him for a thousand years; and he cast him into the bottomless pit, and shut him up, and set a seal on him, so that he should deceive the nations no more till the thousand years were finished. But after these things he must be released for a little while. And I saw thrones, and they sat on them, and judgment was committed to them. Then I saw the souls of those who had been beheaded for their witness to Jesus and for the word of God, who had not worshiped the beast or his image, and had not received his mark on their foreheads or on their hands. And they lived and reigned with Christ for a thousand years. But the rest of the dead did not live again until the thousand years were finished. This is the first resurrection. Blessed and holy is he who has part in the first resurrection. Over such the second death has no power, but they shall be priests of God and of Christ, and shall reign with Him a thousand years.

This millennial reign is essentially the "first phase" of the kingdom of God on the earth (more information can be found in the article The Kingdom of God was the Emphasis of Jesus and the Early Church).