The Four Fixed Signs Of The Zodiac And The Four Beasts in The Book of Revelations
They're grouped in a quadruplicity known as the quality. The qualities are cardinal, fixed ...
Each of the fixed signs creates stability through the vehicle of their element. For Fixed fire (Leo)this can mean a career of self-expression, and ongoing respect in their chosen fields. For fixed water (Scorpio), permanence is found through achievement, and going deep into the timeless mysteries of the imagination, dreams, primal sexuality.
As fixed air, Aquarius fixes on a continuum that reaches into the future, and can doggedly push for reform, or spend a lifetime on their personal inventions. For fixed earth, Taurus digs into the earth, builds with real elements to construct a solid life.
It is also a coincidence that the signs were in the Book of Revelation:
"And the first beast was like a lion, and the second beast like a calf, and the third beast had a face as a man, and the fourth beast was like a flying eagle. (Revelation 4:7)"