two o'clock
The latter should have had with him D'Erlon 's corps of twenty thousand men , and forty-six guns , but these were suddenly withdrawn by Napoleon when the latter found that the Prussian force was stronger than he had expected . They had just reached the field of Ligny when an order from Ney again caused them to retrace their steps to Quatre Bras , where they arrived just after the fighting there had come to an end . Thus twenty thousand men with forty-six guns were absolutely thrown away , while their presence with either Napoleon or Ney would have been invaluable . Soon after two o'clock Picton 's division , which headed the column , heard several cannon shots fired in rapid succession , and in another minute a perfect roar of artillery broke out . The battle had evidently begun ; and the weary men , who had already marched over twenty miles , straightened themselves up , the pace quickened , and the division pressed eagerly forward . A few minutes later an even heavier and more continuous roar of cannon broke out away to the left . Napoleon was attacking the Prussians .