A day of darkness and gloom, a day of clouds and blackness. Like dawn spreading across the mountains a large and mighty army comes, such as never was of old nor ever will be in ages to come.
NIV
A day of darkness and gloom, a day of clouds and of thick mists and darkness, like the morning dawn spread upon the mountains; so there comes a [heathen, hostile] people numerous and mighty, the like of which has never been before and shall not be again even to the years of many generations.
AMP
A day of darkness and of gloominess, a day of clouds and of thick darkness, as the morning spread upon the mountains: a great people and a strong; there hath not been ever the like, neither shall be any more after it, even to the years of many generations.
KJV