Bone and Steel
Capricorn is upright, firm, and rigid. It aids the human in standing up straight, fully bipedal. The individual's position in the world is determined by Capricorn, Saturn, and the tenth house. Social and political systems, in order to function at their best, rely on healthy Saturn influences as well.
But suppose the skeletal matrix weakens somewhat. Aries might be called upon to steel it up.
It makes sense. Old age, ruled by Capricorn, sometimes brings too brittle bones, which are weaker and subject to breakage. Aries begets youth, strength, and flexibility. Sometimes the oldsters even get metal replacement parts.
It's a generational thing, synergistic at times.
Aries square Capricorn. Steel in the spine, one might say.