Gemini 1

The Gemini sign is based of of Castor and Pollux who are—you guessed it—twins. Weird thing is they both have different fathers. Weirder still, this is something that is totally biologically possible. A quick something search and a visit to babycenter.com told me that twins can be "bipaternal". Crazy.

Castor's father was tne the king of Sparta and Pollux's was Zeus. After a life of many adventures, mortal Castor was at the end of his rope. Pollux begged Zeus to kill him rather than live forever without his brother. Moved by the display of brotherly devotion Zeus decided to grant Castor immortality. Now the two live in the sky for all eternity.

Makes you think about how you treat your siblings now, hmmm?

The two are often depicted as helmeted horsemen wielding spears, which gives good reason for this composition. Interestingly, twin horsemen also appear in Germanic, Lithuanian, and Indian traditions.