A French documentary claims Napoleon was confused on the battlefield by a mistake in the map he used to plan his strategy.

Battle of Waterloo
© Carle Cernet / Bovinet
The Battle of Waterloo
A mistake in the map Napoleon Bonaparte used at Waterloo was a key factor in the 1815 defeat that crushed the French Empire and ended his military and political career.

According to a documentary broadcast on French television Monday, Napoleon was confused about the position of the Duke of Wellington's forces because of a map error of one kilometre (more than half a mile) introduced by the printer.

Consequently, he aimed his artillery at the wrong location and his cannon balls fell woefully short of the British, Prussian and Dutch lines.

The documentary-maker, Franck Ferrand, said: "Napoleon was relying on a false map for his strategy in his last battle. This explains why he mistook the lie of the land and was disoriented on the battlefield. It is certainly one of the factors that led to his defeat, although not the only one."

Mr. Ferrand explained: "The strategic farm of Mont-Saint-Jean is shown one kilometre from its real location. One kilometre was the range of his cannons so you can see what a difference it must have made."

Maps
© Telegraph
The original, hand-drawn map on the left shows a different location for Mont St Jean than the printed versions on the right.
The false map was discovered by a Belgian illustrator and historian, Bernard Coppens, who advised Mr. Ferrand on the documentary.

Mr. Coppens unearthed the map, still stained with blood and identical to the one Napoleon himself was using, at a Brussels military museum.

"We compared the printed map used on the battlefield with the original hand-drawn one it was copied from," Mr. Ferrand said. "We realised it was a printing error. Not only was the farm in the wrong place, but the map showed a bend in the road that did not exist."

Asked if the outcome would have been different if Napoleon had been equipped with a more accurate map, Mr. Ferrand said : "We also found a letter from his younger brother, Jerome Bonaparte, which described him as looking completely lost on the battlefield of Waterloo and no longer being in full possession of his faculties. He was a shadow of his former self."

Napoleon also underestimated the Duke of Wellington and failed to issue clear orders to his commanders, Marshall Ney and General Grouchy.

Their blunders on the battlefield have also been blamed for the defeat, although the 19th century Swiss military writer, Antoine-Henri, Baron Jomini, praised "the aplomb and sang-froid" of the Duke of Wellington and his commanders, and the "firmness" of the British infantry who formed squares and resisted the French cavalry charges.

Mr. Ferrand said Napoleon had been undermined by his exile on the Isle of Elba, and had tried to commit suicide by drinking a vial of opium just over a year before Waterloo.

"We also discovered documents showing that Napoleon was threatened when he was on the Isle of Elba, in plots that were masterminded by his former diplomatic aide, Talleyrand (Charles Maurice de Talleyrand-Périgord)," he said.