In astrology , Aries is the first sign of the zodiac , considered as governing the period from about March 21 to about April 19. Its representation as a ram is identified with the Egyptian god Amon and, in Greek mythology , with the ram with the golden fleece , on the back of which Phrixus , the son of King Athamas , safely fled Thessaly to Colchis , where he sacrificed the ram to Zeus , who placed it in the heavens as the constellation . The ram’s golden fleece was recovered by Jason , leader of the Argonauts .