(from The Divine Institutes, c. 320 A.D.)
“God completed the world and this admirable work of nature in the space of six days, as is contained in the secrets of Holy Scripture, and consecrated the seventh day, on which He had rested from His works. But this is the Sabbath-day, which in the language of the Hebrews received its name from the number, whence the seventh is the legitimate and complete number.”
“Therefore, since all the works of God were completed in six days, the world must continue in its present state through six ages, that is, six thousand years. For the great day of God is limited by a circle of a thousand years, as the prophet shows, who says, “In Thy sight, O Lord, a thousand years are as one day” (Ps. xc. 4). And as God labored during those six days in creating such great works, so His religion and truth must labor during these six thousand years, while wickedness prevails and bears rule. And again, since God, having finished His works, rested the seventh day and blessed it, at the end of the six thousandth year all wickedness must be abolished from the earth, and righteousness reign for a thousand years; and there must be tranquility and rest from the labors which the world has now long endured.”
End-Times Eschatology 