But Cato knew instantly what the sound was and his stomach knotted in icy terror. He glanced towards the Emperor, staring up the vale, a spoon heaped with jelly halfway to his mouth. As Cato turned back he saw a dark liquid mass, gleaming and foaming, sweep round the bend in the vale, smashing down the stunted trees that clung to the steep slopes, dislodging boulders and mounds of earth, carrying all before it. The vast body of water that had been held back by the final dam roared out of the vale, directly towards the imperial party and its escort.

CHAPTER TWENTY

At first no one moved. Every man was too horrified by the sight of the churning wall of water sweeping towards them. Tigellinus acted first. He cupped a hand to his mouth and yelled, ‘Run! Run for your lives!’

The cry broke the spell and the imperial retinue, the engineers and the Praetorian guardsmen began to flee, some heading directly away from the water, while most tried to escape to the side where the ground rose slightly. Cato threw down his shield and spear and snatched at his chinstraps. Macro did likewise, already moving away from the wave.

‘Wait!’ Cato called to him. ‘We must save the Emperor!’

Macro paused, then nodded and they turned towards the table and the cake. Claudius was stumbling towards the river as fast as his limp would allow, casting terrified glances back over his shoulder as the wave approached. Tigellinus was racing across the ground after him and Cato saw, with a stab of fear, that the centurion might reach the Emperor first. He struck out, sprinting as fast as his legs would carry him, still weighed down by his scaled armour vest. Macro ran after him. A strong breeze rippled the folds of the Emperor’s toga and the loose strands of his hair as the wave thrust a cushion of air ahead of it. The hissing roar of the pounding water seemed deafening to Cato as he ran at an angle towards Claudius. To his left he could see that Tigellinus was gaining ground and would reach the Emperor first. His dagger was grasped in his hand, point held low and level as he single-mindedly sprinted towards his prey.

The air felt cool at Cato’s back and he risked one last glance towards the wave and saw that it was no more than fifty feet behind him, an ugly churning mass of spray and brown water carrying brush and trees with it. There was a cry of terror and despair away to his right as the first of the Praetorians went down, and then the voice was instantly silenced as the man was submerged in the tumult.

Ahead, Tigellinus was no more than ten feet from the Emperor, and then he stumbled, the toe of his boot stubbing against a rock. He fell down, the dagger spilling from his fingers. Cato ran on, calling out, ‘Sire!’