A Princess of Mars (Unabridged‪)‬

While fleeing from a band of Apache warriors, Civil War veteran John Carter hides in a sacred cave, where he is mysteriously transported to Mars. Now endowed with superhuman abilities due to the low Martian gravity, he becomes embroiled in a conflict between the six-limbed Green Martians and humanoid Red Martians and meets the beautiful Dejah Thoris. 

This is book one of Edgar Rice Burroughs' Barsoom series.