Michelangelo, Prisoners, or Slaves. Photograph: George Tatge/CORBIS
Michelangelo's Prisoners, or Slaves, were begun for the tomb of Pope Julius II but never finished. In its entirety – including the Dying and Rebellious Slaves in the Louvre and the statue of Moses on the final, reduced version of the tomb eventually erected in Rome – this constitutes the greatest unfinished masterpiece in the world. Yet Michelangelo did not leave things unfinished out of laziness. It is an aesthetic choice. The tragic power of these prisoners as they struggle to emerge out of raw stone is an expression of the human condition that equals Shakespeare's Hamlet.
• Accademia Gallery, Florence