On the symbolism of warriors, Tartarus and the west.
The warrior is the one in close connection to the rebirth aspect because he was closely linked to death itself. Through their heroic actions they are immortalized and thus reborn quickly.

This is fairly well seen in the written forms. Breastplate of warriors was connected to death in ancient Greece and Egypt. The name for breastplate in anc. Greek was "thorax" and it is frequently found drawn two times in a row in tablets.

It was Robert Graves that proposed "tar" meant "west" in Minoan, as can be seen in cities at the west point of the island. Drawing the double form of "thorax" could hold a more ancient meaning of thor-thor or Tartar. The west point where souls go after death.

Tartarus would then hold a meaning of west-west. The west was seen as the land of the dead, a place where souls go after dying just like the sun "dies" in the west every evening. This wasn't just in religious or mythological context, literal west was seen like this, too.

This is even more reinforced when we look at the Etruscan word for a tomb - tauru. Further more, it connects "taurus", the bull, the ancestral life force, with the tombs.

The inversion of the breastplate sign, which is sometimes seen, would hold a meaning opposite of west-west which is the uttermost east, the land of rebirth of the sun. That is why we have Mithra coming from the east, because he is being reborn like the "invincible sun".

This shows that ancient people saw world through its symbolic meaning and they implemented these symbols into their everyday life. Warriors are connected to the west, to the land of the dead, because they are at the high risk of dying.

Similarly so, it's not a coincidence that a double breastplate could be a symbol of Tartarus. Breastplates are seen the most on the warriors and dead warriors which symbologicaly connects them to the world of the dead and thus they became the word for it.