“The tree walls symbolize the three phases of the Work, which begins in spring under the zodiac sign of Aries and the decaying corpse. In summer, in the sign of Leo the conjunction of sprit and soul occurs, and  in December, in the sign of Sagittarius, the indestructible, red spirit-body emerges, the elixir or the ‘drinkable gold of sternal youth’.” ——< Alchemy & Mysticism>

According to the three period of time It is not difficult for us to find out that Aries, Leo and Sagittarius they both belong to the fire element in astrology. Fire has a symbolic extension in addition to its physical function.