In early May, the Xianbei Cavalry Regiment began obeying Murong Chui's earlier strict orders, immediately withdrawing from the banks of the Huai River and choosing a route that kept as far from the waterways as possible.
They had not underestimated the speed of the May Rains' advance. Their response was swift and their measures correct, yet they had still underestimated the crushing advantage the weather possessed... The so-called spread of the rainy season was not as simple as a visible, orderly progression from south to north, as though it would not move north until the south had received its proper share. That was merely a graphic summary of the probability distribution of rainfall.
In fact, after only a day's march, the Xianbei discovered to their astonishment that it had begun raining to the north before any rain had fallen behind them toward the Huai River.
The ordinary Xianbei cavalrymen were all right. They did not know what this meant and took it for ordinary rain. But the senior commanders, led by Lan Jian, instinctively felt their hearts quiver. They knew they had already made a grave mistake: they should never have tried to attack that stone fortress at Wokou. Still, they ordered the troops to ignore it and march north through the rain, hurrying back. They no longer hoped to reach Chenliu; at the very least, they had to get back to the vicinity of Chen Commandery first.
This was, of course, an entirely correct strategy. It was like escaping an encirclement: never mind whether the immediate circumstances were good or bad. The right thing was to stake everything on maintaining speed and getting out.
Run for their lives, escape the overlap between enemy-controlled territory and the rainy season as quickly as possible, and everything else could be dealt with.