On September 13, 1501, Michelangelo Buonarroti set to work on a block of Carrara marble that had been lying in the yard of the Opera del Duomo in Florence for decades. Three years later it was the David. He was 26 and had finished the Pieta in Rome the year before.
The block was the problem and the attraction. It had been quarried for a colossal prophet intended for one of the cathedral's buttresses, and it was over five metres tall and shallow, less than a metre deep, because it had been cut for a figure standing against a wall. Duccio got it in 1464. He stopped within weeks. He had roughed out the legs and damaged the stone. Antonio Rossellino was contracted in 1475. He gave it up. For twenty-five years it lay in the open, and one end had weathered.
That shape is why the David is what it is. A figure designed to stand in a niche or against a wall has to be seen from the front, and Michelangelo's solution was to make the body do the turning: the head looks left, the left arm crosses the body, the weight is on the right leg, and the whole figure is arranged so that the front view contains the movement that would normally need the viewer to walk around it. The proportions are not classical either. The head and hands are large, and the reason is that the statue was going to be looked at from below, from the piazza.
The commission came from the cathedral works, which had been trying for years to find someone to take the block on, and the contract, signed on August 16, 1501, gave him two years. It was the first large-scale marble sculpture carved in Florence since Donatello, and the workshop practice of finishing every surface by hand, including the back, was unusual for a figure meant to go against a building.
He was paid 400 gold florins. The finished statue was unveiled in front of the Palazzo Vecchio on September 8, 1504, and it has been argued about ever since, mostly over where it should stand and who owns it.