Agrippina pointed out a mother duck who serenely swam down the river’s centre followed by a line of her young, their formation as orderly as a Roman legion. ‘All this nonsense doesn’t even frighten the ducklings,’ she said dryly.

‘Perhaps it makes these big men feel better about themselves,’ Braint murmured.

Nectovelin said, ‘And Caratacus?’

‘There.’ Braint pointed.

The two princes stood knee-deep in the water, working their way through a heap of weaponry. They destroyed each item, snapping dagger blades, bending swords in two, smashing shields with axes, before hurling the pieces into the deep water. Agrippina saw a priest close to the princes; the druidh held his hands out wide, as if to embrace the river itself, and he chanted as the princes worked.

Amid the ludicrous spectacle of the posturing warriors, Agrippina found this ceremony dignified, oddly moving. Her own people, farmers, had similar rituals in which you offered the gods household objects like cups, bits of clothing, farm tools like ploughs. You placed them in gaps, like ditches and doorways and river banks - places between worlds, where reality came unstuck. These were sacrifices to the gods, pleas for the continuing cycle of the seasons - and, today, pleas for victory and honour in war. And as he destroyed his iron weapons Caratacus built on a still more ancient ritual yet. It was the closure of a circle of life, for some believed that metal, born in fire, was alive, and that it was fitting that it should at last ‘die’ in water.

But Agrippina saw that among the gifts being offered to the river were Roman goods: Samian crockery, finely worked Gallic daggers and swords, even coins no doubt adorned with the invading Emperor’s head. Even in this most sacred of British rituals, she thought, the Romans had already gained a foothold.

A runner approached Togodumnus, evidently bearing bad news. The prince swore, hurled away the last of his offerings, and stomped out of the water. His brother, Caratacus, continued with his patient ceremony.

Cunedda murmured, ‘Togodumnus may pay for that. It doesn’t do to turn your back on the gods.’

‘Probably he’s been told that the Dobunni have laid down their arms to the Romans,’ Braint said laconically.

Nectovelin snapped, ‘Gods, woman! If you were Greek I’d call you an oracle.’

Braint shrugged. ‘I just listen to what people say.’

Cunedda asked Nectovelin, ‘If things go badly today, what will become of everybody - the old people, the women and the children?’

Nectovelin grunted. ‘The Romans haven’t crossed an Ocean to be merciful. They’ll be looking to strike a blow that will resound throughout the island. We may still be able to stop them doing that, even without the Dobunni. But it’s in the hands of the gods.’

Agrippina asked softly, ‘But, Nectovelin, your Prophecy - has it no news of what will happen today?’