The Abandonment of Mars

The Abandonment of Mars, also known as the Great Diaspora of the Ice Warriors, was the series of events that lead to the Ice Warriors leaving Mars as it became inhospitable. (PROSE: Red Planet) Accounts differ as to when the downfall of the Ice Warriors took place, with some mentioning being at their peak and active thousands of years BC, (TV: Cold War, Empress of Mars) and others claiming their atmosphere to have been destroyed "centuries" before the 21st century, (AUDIO: Red Dawn) or even millions of years BC. (AUDIO: Deimos)

History
After Mars was lost, the Ice Warriors sent out eleven World-Ships to find a new homeland for the species. However, High Marshal Kryss' World-Ship, the lead vessel of the flotilla, was separated from the rest of the World-Ships due to the cosmic storm the Great Desolatrix, and the World-Ship crash landed. Kryss spent seven days protecting it from those who tried to scavenge from it, but he was eventually captured by the Sycorax who took him to an asteroid to fight in the Cage. He was eventually rescued by the rest of the World-Ships after the Fourth Doctor used the long-range comms to contact the fleet. (PROSE: Red Planet)