Mars (Ares) is the Roman god of war, therefore astrology takes it as a symbol for aggression,
animosity, brutality and a strong will. The more positive aspects of Mars are courage, power and
uncompromising steadiness. In standard astrology Mars is the ruler of Aries and Scorpio, while he
was rather connected to
Sagittarius in old
Little attention is paid to the fact that the day of Mars (March 15th), celebrated in all of old Rome, happened to be the same day (and the same feast) as the beginning of spring.
In Tarot, Mars is often connected to the Tower,but also to Passion (Strength), adding a sinister touch to the latter.
Mars was always seen as an aggressive, malevolent planet, perhaps due to its reddish colour which provoked associations to fire and blood. The planet was also seen as the ruler of metal, particularly iron, and the forging of it. What is almost forgotten today is that blacksmiths - those who could forge or rather 'master' metal - were long watched with cautious awe, almost as if they were sorcerers. In Mongolian lore this belief lasted well into the 12th century AD, Mongolian shamans often used to carry several pieces of metal with them to demonstrate their mastery over the powers of the earth. Ghengis Khan was a former blacksmith and as such he had a reputation of being something special long before he conquered half the world.
In ancient Mesopotamia Mars was equated with Nergal, the sinister god of the underworld, of death, destruction, pestilence and other less delightful things. A war god was he but more the darker side of a war, when evil enemies raided the lands. On the other hand, he was also seen as the Judge of Souls and the Lord of Justice, ruler of the limits of the created world. Depicted as a bull with a human head one of his names was 'The Bull of Heaven', other images showed him as a creature with a lion's body and wings.
As the Lord of Limits and God of Necessity Nergal bears a striking resemblance to the Sephiroth Geburah which - not accidently - is ruled by the planet Mars. Like Geburah balancing and limiting the overwhelming powers of Chesed (associated with Jupiter) Nergal puts limits and restrictions to the created world - not always appreciated but nonetheless necessary. It is quite interesting to think a bit further about this and not simply take Mars for the rather one-dimensional picture of a destructive war god.
The Greek war god Ares - direct model for the later Roman Mars - lost the deeper aspects of Nergal and became a pure war god, with the focus rather on the brutality of war than its more heroic facets which were more associated to, say, Pallas Athene or Jupiter. Like all Greek gods Ares was a regular protagonist in all kinds of entertaining stories, most famous his neverending love story with Aphrodite (Venus) in which he didn't play the most heroic role and was frequently outwitted by Hephaistos.
The Roman war god Mars originally developed from the earlier Etruscan Maris, the god of fertility and agriculture, which might explain why his festival day in old Rome - the Ides of Mars on March 15 - fell on the beginning of spring. With the expansion of the Roman Empire and the rising importance and glorification of the military Mars was increasingly equated with the Greek Ares and celebrated as a war god. Unlike Ares he was a flawless hero with no short-comings and his cult was immensely popular, second only to Jupiter.