Michelangelo worked on it from 1552 until the last days of his life, in 1564. In his dying days, Michelangelo hacked at the marble block until only the dismembered right arm of Christ survived from the sculpture as originally conceived. It has also been suggested that the sculpture should not be considered unfinished, but a work in a continuous process of being made visible by the viewer as he or she moves around to see it from multiple angles. (Wikipedia)