The complete origin of the Green Martians is mostly unknown. They first appeared in the waning days of the White Martian races, when the oceans began to recede, and began raiding the Orovar and Lotharian cities, driving these once-great civilizations into increasingly remote regions. When the White races abandoned the cities, the Green hordes took over. Though they appear to have lacked the intelligence to make use of most of the ancient technology left behind, their size, brute strength, and abundance of limbs for many years prevented them from being driven out.