The rider came through the rear of the formation at the pace of an animal pushed hard from a long distance.
He threaded between the horses of the rear ranks, his mount's sides heaving, and reached Batu's position.
"They're in the water," he said.
Batu raised his hand.
The signal went through Penk's relay across both formations simultaneously, carried by the riders already in position across the full width of the line.
The pace changed. A push, committed and hard, the kind that does not slow for what falls ahead of it, and the sound of it rose up through the frozen ground and into every rider on the line.
Thousands of horses going from the sustained cycling advance into a forward drive, the mass of the whole in motion at once.
Berke's south bank saw it.
The fire intensified.
The south bank had been managing its rate through the full duration of the fight. Now it released everything.
