On 18 June 1815 the armies Napoleon and the Duke of Wellington, each of approximately equal strength, faced one another in southern Belgium to fight one of the most decisive battles in history, while elements of a third, Prussian, army sought to reach the field in time to turn the tide in favour of the Allies. On the outcome of Waterloo hung the fate of Napoleon's renewed bid to impose French rule over Europe. To understand what happened and why - read on.