The engineer bowed his head again, and then began to talk through the procedure he had devised to drain the Albine Lake. Cato listened as best he could to the engineer’s lecture but his eyes were fixed on Tigellinus. The centurion stood at the head of the century, no more than fifty feet from the Emperor. His hand was resting on the pommel of his sword, his fingers drumming against the sword handle. Between him and Claudius stood a loose screen of German bodyguards. The Emperor was safe for the moment, Cato decided.

Apollodorus gestured down the vale leading to the river. ‘As the Emperor can see, I have ordered the construction of a series of dams, each with a sluice, so that we can control the flow of water as we drain the area around the lake. If we had simply cut a channel from the lake to the river, as I believe your adviser, Pallas, originally suggested, then we might well have caused the Tiber to overflow and flood the centre of Rome as the main body of water reached the city.’

Narcissus chuckled. ‘Not one of my friend’s finer moments, alas. Still, Pallas has his talents, whatever they may be.’

‘Quite right.’ Claudius nodded. ‘My wife, the Empress, rates him highly indeed.’

Macro whispered. ‘Oh, I’m sure she does.’

‘Shhh!’ Cato hissed.

The engineer led the way down the track that had been cut into the slope of the vale. Every half mile or so was another dam, behind which the water flowing out of the lake filled an expanse of the vale. Late in the afternoon the procession finally reached the last and biggest of the dams. At its foot a small stream flowed round a curve in the vale, the sides of which were appreciably steeper than up by the lake. The stream was fed by a culvert dug round the end of the dam. A handful of workmen stood off to one side, loading unused timber on to a wagon. They briefly bowed towards the Emperor and then continued with their task.

Apollodorus paused at the base of the dam where long, thick lengths of timber braced the stakes driven vertically into the ground. A number of ropes had been tied round the central buttress timbers and led up to the sides of the vale where they were fed through large pulleys, secured to stakes.

Narcissus looked up warily at the dam towering some fifty feet above him. ‘Are we quite safe here?’