Michelangelo's system of working was as powerful and original as his art. Before he began a statue he could already discern the finished masterpiece lurking within the rough-hewn block of marble, which he would attack with reckless assurance, great splinters flying in all directions as he feverishly cut away the waste stone, and saw the figure spring slowly into life under his magic chisel. A contemporary, writing in 1550, when Michelangelo, then seventy-five years of age, was carving the _Pietà_ which he intended for his tomb, thus describes the master at his work: "I have seen him, although over seventy years of age and no longer strong, cut away more splinters from a block of very hard marble in fifteen minutes than three young men could have done in a couple of hours, and with such fierce recklessness that I thought the whole work must fall to pieces. For he knocked off splinters the size of a hand, following the line of his figures so closely, that the slightest mistake would have irreparably spoilt the whole group." In one of his finest sonnets Michelangelo mentions this wonderful gift of the true artist to penetrate dull marble and to perceive, as through a veil, the perfect work of art within: Non ha l' ottimo artista alcun concetto Ch' un marmo solo in se' non circoscriva Col suo soverchio; e solo a quello arriva La mano che ubbidisce all' intelletto. Even such colossal works as the _David_ were carved by Michelangelo directly from the marble, without previously modelling a full-size clay figure. In none of his finished masterpieces, however, is it possible to observe Michelangelo's methods better than in the unfinished statue of Saint Matthew, now in the Academy, Florence, which, although little more than a rough-hewn block of marble, already reveals all the power and beauty of the perfect work of art. When quarrying marble at Carrara for the façade of San Lorenzo, he could tell to a nicety the exact measurements of the blocks required, although he had not yet prepared a model or even accurate drawings to guide him in his work. The whole monument was already complete, even to its minor details, in his mind.