In early 1503 Leonardo agreed to paint a huge mural in the Palazzo della Signoria in Florence. The painting was to depict the Battle of Anghiari, a celebrated victory of 1440 against Milanese forces. More than any other composition of Leonardo's career, the Battle gave full rein to his interest in the depiction of powerful emotion. In this preparatory drawing he studied the expressions of fury in man and horse (and, for comparative purposes, a lion). Work on the Battle of Anghiari proceeded with interruptions until 1506, when Leonardo was allowed to travel back to Milan. He never returned to the Battle, and only the central portion of the painting was completed. This was covered over by Giorgio Vasari's frescoes after 1563; recent attempts to locate Leonardo's mural beneath Vasari's work have been inconclusive. On the other side, a compilation of sketches, notes and diagrams includes a pre-Copernican diagram of the solar system, with the earth at the centre, the moon in the inner orbit, and the sun in the outer orbit. Projected lines show how the relative positions of sun and moon give the phases of the moon as seen from the earth. A similar demonstration is seen in the opposite corner, though that diagram was cut when an early owner trimmed the sheet to 'improve' the presentation of the horse studies on the other side.