Laberius kept alongside him, and they exchanged the usual empty pleasantries, asking after relations and friends. Hadrian sensed that the former consul wanted something, but manners dictated that they chat about nothing first.

‘You are off to the army soon.’ It was a statement, not a question.

‘I am.’ Hadrian was conscious that he slurred some words and cursed himself for doing it now, especially when Laberius gave a faint smile. Men said that it was the accent of Hispania, but since Hadrian had spent barely a year in the province and only when he was already fourteen, he doubted it.

‘You do not care for the courts?’

‘Acting as judge may teach a man something,’ Hadrian conceded, ‘although it seems largely a question of discerning which side is lying the least.’

This time Laberius’ smile had less mockery. ‘A good training for life, I should have thought. Still, soldiering may be a little more straightforward. The Minervia have earned a fine reputation in what is still a short history. It is a good command, albeit a scattered one at present, as you have no doubt learned from your investigations?’ He paused, and stared straight into Hadrian’s eyes. ‘That is unusual diligence – or something else perhaps? Still, I am sure you know your own business.’

Hadrian had expected the matter to be raised at some point during the evening, and wondered only how soon and who would bring it up. The emperor had surely learned of his visit to the camp of the foreigners before the day was out. It was probably better that someone was speaking openly to him about it.

‘I wish to serve the princeps and Rome well.’

‘Indeed, and such an honourable intent must be praised. But why talk to the frumentarii?’

This time Hadrian smiled. ‘Because I wonder whether we do not take sufficient advantage of their knowledge. Where else in Rome will you find men from every legion, recent arrivals most of them and sent back in due course? Apart from the lists of numbers, locations and supplies, those men have knowledge and news beyond the written reports of legates and procurators. They could all become eyes and ears, reaching out across the globe.’

Laberius was sceptical. ‘Common soldiers, though. I’ll grant they can all read and write in a good hand, but they are not selected for intelligence or insight.’

‘But they could be.’

The former consul nodded several times, his head moving slowly as if it confirmed an obvious truth, but Hadrian could tell that he was thinking. A lot of good ideas appeared so simple once someone had explained them, and there was no doubt that Laberius Maximus was now exploring the possibilities.

‘That is original,’ he conceded at last. ‘Although perhaps we should be cautious in turning so many simple soldiers into spies. The gods only know how much they might discover, and how inconvenient it might prove.’

‘For the good of the res publica.’

‘An expression frequently employed by the last of the Flavians – as even you may be just old enough to recall – so of meagre comfort. After all, we all have our little secrets, do we not?’ The stare was intense. ‘And would prefer that they remain just that, harmless indiscretions known only to ourselves. Trust is important. To trust the men picked by the emperor or appointed by the Senate to do their jobs to the best of their ability, without having to be told step by step how to go about them. A degree of ignorance does little harm if it fosters trust.’