Mars in Libra

Opposite Aries sits Libra, so by the rule Alan Leo states in How to Judge a Nativity (before 1917), this is a detriment for Mars. The word means the sign across the circle from a planet's own house and carries no verdict on a chart. Lilly 1659 names Libra for it directly.

Libra is also the chief house of Venus in Lilly's words, and Ptolemy (Ashmand's 1822 translation) gives Venus a temperate nature where Mars is chiefly dry and burning. The two planets are set up as contrasts throughout the old books, one counted among benefics and the other among malefics, labels for the temperaments each was thought to carry. Ptolemy also shuts Mars out of the triangle of Gemini, Libra and Aquarius.

Lilly allows Mars only degrees 25 to 30 of the sign as his terms, and Libra, being hot and moist in his table, shares just the heat. Modern popular astrology often reads this as conflict handled through negotiation, or anger held back for the sake of fairness. Those are modern phrasings with no counterpart in the old texts consulted here.