The constellation is old. In the Babylonian star lists it is MUL LU-HUN-GA, the Hired Man or Hired Labourer, and the shift to a ram appears in the later tradition; the Greek figure is the ram of the golden fleece sought by Jason and the Argonauts, whose fleece hung in the grove at Colchis. The twelve equal signs of thirty degrees each, as distinct from the ragged constellations, are a Babylonian invention of roughly the fifth century BCE, adopted into Greek astrology and transmitted from there.
Because the equinox drifts slowly westward against the stars at about one degree every seventy-two years, the sign of Aries and the constellation of Aries no longer coincide: the tropical zero point now lies in the stars of Pisces. Western astrology keeps the seasonal frame and Indian astrology keeps the stellar one, which is the root of the sidereal and tropical difference between the two systems, and the discrepancy is a fact of astronomy rather than a dispute either side can settle.