He had no great intellect, and cheerfully admitted he had not.

From Waterloo A Near Run Thing by David Howarth. Page 99.

Among his equals, he could seem disarmingly modest, and was always disarmingly trusting. He kept his own promises, and took it for granted that everyone else would keep theirs. He had no great intellect, and cheerfully admitted he had not. At formal parties, he was inclined to entertain or embarrass the guests by making up childish riddles, and he was vastly amused when the University of Oxford offered him an honorary doctorate of law. ‘If they make me a doctor,’ he said, ‘they’ll have to make Gneisenau an apothecary. He’s the man who administers the pills I prescribe.’ It was hard to be sure if he knew there was more than one kind of doctor.

Gneisenau in fact, as his chief of staff, was just the counter­ balance he needed: dour, efficient and chronically suspicious, he was always at hand to examine and criticize the promises the marshal gave and accepted so heartily. Wellington’s promise had been a case in point. Did Wellington really mean to stand at Waterloo? Was he able to do so? If he found himself in difficulties, would he not put British interests first, pull out and leave the Prussians in a fatal situation? It was said that Gneisenau and Blücher had had an angry argument. Blücher did not always overrule his chief of staff, but he had done so then; and the sound of the massive cannonade proved that this time his trust had been well placed.

Bruised by the fall from his horse at Ligny, and still suffering from the shock of it, he marched with his army all the morning, urging them on when their guns and transport bogged down in the muddy lanes. When he made his promise, he had not reckoned with such lanes. After the night of rain, the main roads that the British and French had used were bad enough: the Prussians were trying to use the cross-lanes, which at their best were only built to carry farm traffic from one village to another. The Prussian troops the Emperor had seen in the middle of the morning were only a vanguard. By the middle of the afternoon, a Prussian force was in action against the French in the village of Plancenoit, to the east of Rossomme. But the main body was still filtering slowly, one wagon at a time, through waterlogged valleys out of sight of the battlefield. Wellington did not know where they were, or whether they would really come in time to fight before the day was over. He only knew that Blücher had promised a thing it was supposed no army could ever do: to fight a major victory before it had recovered from a serious defeat.