History of the Millennium
o Jewish Origins
Millennium, Encyclopedia Britannica, eleventh edition, page 459
In six days God created the world, on the seventh He rested. But a day of God is equal to a thousand years (Psalm 90:4). Hence the world will last for six thousand years of toil and labor; then will come one thousand years of Sabbath rest for the people of God in the kingdom of the Messiah. This idea must have already been very common in the first century before Christ.
Eschatology, The Jewish Encyclopedia, V, page 211
The present world of toil is to be followed by a Sabbatical millennium, the world to come. Of these the six millenniums were again divided, as in Parsism, into three periods: the first 2,000 years devoid of the law; the next 2,000 years under the rule of the law; and the last 2,000 years preparing amid struggles and through catastrophes for the rule of the Messiah.
o Early Christians
Barnabas, Epistle of Barnabas (100 AD)
Of the Sabbath He speaketh in the beginning of the creation; And God made the works of his hands in six days, and He ended on the seventh day, and rested on it.
In six thousand years the Lord shall bring all things to an end; for the day with Him signifieth a thousand years; and this He himself beareth me witness, saying, Behold, the day of the Lord shall be as a thousand years. Therefore, children, in six days, that is in six thousand years, everything shall come to an end. And He rested on the seventh day. This he meaneth; when His Son shall come, and shall abolish the time of the Lawless One, and shall judge the ungodly, and shall change the sun and the moon and the stars, then shall He truly rest on the seventh day.
Irenaeus, Against Heresies (180 AD)
For in as many days as this world was made, in so many thousand years shall it be concluded. And for this reason the Scripture says: Thus the heaven and the earth were finished, and all their adornment. And God brought to a conclusion upon the sixth day the works that He had made; and God rested upon the seventh day from all His works. This is an account of the things formerly created, as also it is a prophecy of what is to come. For the day of the Lord is as a thousand years; and in six days created things were completed: it is evident, therefore, that they will come to an end at the sixth thousand year.