Michelangelo’s 'David' was carved from a single block of marble that had been deemed defective and abandoned by other sculptors for how many years?

40 years

The block was first worked in 1464, about 37 years before Michelangelo’s 1501 commission—not 40 years of uninterrupted abandonment—and Antonio Rossellino made another attempt in 1475. Despite the marble’s flaws, Michelangelo transformed the difficult block into an emblem of the Renaissance.