A primitive and devout civilization was carved into the dust-filled canyons of Mars. These aging and severely eroded habitations miraculously remain intact, regardless of how much Grineer machinery has been fastened to it. Rusty metal and oil-soaked sand mark the territory of its new proprietors.
The Grineer have reclaimed the abandoned dwellings of an ancient society which sprung up around a massive Orokin terraforming device. Content to make use of existing structures, Mars' current occupants have established a base of military operations in one of the few regions that has a habitable climate moderated by Orokin technology.
Mars was originally inhabited by a civilization that worshiped the golden 'Skymen'. The Grineer eventually invaded the planet in their usual violent manner and exterminated the locals, with Baro Ki'Teer being the only known survivor of the invasion. It is also the possible place of origin of the Inaros Warframe.
An immense object can be seen above the clouds in space; the object appears to be a Grineer Asteroid base and possibly one of Mars's two moons, either Deimos or Phobos. This is quite remarkable for how large the object is seen in space, perhaps making it the largest Grineer mining operation to date.
Although the Grineer are supposed to have recently occupied the planet (or that it is one of their most recent occupations at any rate) there are signs of very old Grineer-like equipment scattered and rusting in some places, this either suggests that the Grineer were previously here before but had to evacuate at some point, or something about Mars rusts and corrodes metals at an accelerated rate.
The planet is littered with massive wind generators, providing what appears to be the majority of the planet's power, and various pumps and water bays are used to filter and process water.
Mars is currently one of three planets, the other two being Earth and Uranus, where wild creatures are encounterable.
Gradivus was one of the gods by whom a general or soldiers might swear an oath to be valorous in battle.
Martialis means "from Mars".
Olympus was the home of the Greek Gods in Greek mythology, it's also the name of the Highest mountain on Mars and in our solar system: Olympus Mons.
A Spear is a pole weapon consisting of a shaft with a pointed head which became the standard weapon of Roman legionaries for a period of time.
Ultor is named after one of Mars' epithets, Mars Ultor ("Mars the Avenger" in Latin).
War reflects Mars' role as the Roman God of War.
The fact that both the Corpus and the Grineer are present on Mars is a nod to The Gradivus Dilemma, which ended with the Grineer taking over several nodes originally controlled by the Corpus.
Along with the Infested-controlled Dark Sectors, this makes Mars the first (and so far, the only) planet where all three major enemy factions are present.
Mars was a purely Corpus-controlled planet from Update 14.0 until Update 15.13, when several nodes were given to the Grineer.
When originally released, Mars had the snowy Corpus Outpost tileset as its environment, which did not reflect the red, sandy environment that Mars has. This was fixed in Update 19.0, with the Grineer Settlement tileset replacing Corpus Outpost as the main planetary tileset to better reflect Mars' appearance.
Due to an additional change in the Specters of the Rail update, Fieldron samples drop on this planet, even though the Grineer control almost all the nodes on the planet. Whether this is an inconsistent error, or a nod to the fact that the Corpus used to completely control Mars, is unknown.