'Brother, I beg you. Do as you are ordered!'

'No!'

'The Britons have already sprung their surprise on us,' Sabinus argued desperately. 'And now we – you – can surprise them.'

'No.'

'Vespasian.' Sabinus leaned forward and spoke with quiet intensity. 'Do it! If you stand here you'll be accused of cowardice. Think of our family name. Do you want the Flavians to be remembered as cowards for the rest of time? Do you?'

Vespasian returned his older brother's stare with equal intensity. 'This is not about posterity. This is about doing the right thing. By the book. While the army is disorganised, we must have a standing reserve. Only a fool would disagree. '

'Quiet, brother!' Sabinus glanced round nervously in case Vespasian's intemperate words had been overheard. Vitellius stood to one side and casually raised a hand in greeting.

'Vespasian-'

But the legate was no longer listening. He was staring at the forest, more clearly visible in the thinning mist. Unless his eyes were playing him false, there was movement down there. From under the boughs of the trees at the edge of the forest, briar thickets were slowly emerging in dozens of places. What dark magic was this? Could those devils the Druids conjure up the very forces of nature to aid them in their fight against Rome?

Then the briars were thrown to one side and the true genius of Caratacus' plan became clear. From deep within the forest charged a column of chariots. The thunder of hooves and rumble of wheels was audible even up by the Roman army's camp. The heavy British chariots burst out into the open and charged down upon the artillery positions on the left flank.

The legionaries manning the bolt-throwers had no time to react to the threat and were cut down where they stood, trampled and ridden over by the chariots, or speared by the warriors riding on the chariot beds. In the wake of the chariots swarmed thousands of lightly armed men carrying pikes. They streamed across the rear of the attacking force like grey ghosts in the thinning mist. They paid no attention to the still cohorts of the Second Legion as they rushed to close the trap on Claudius and the main body of his army. More Britons appeared all along the edge of the forest and threw themselves upon the legions' tangled flank. The ferocity of the attack compounded the effect of the surprise and the Britons carved a deep swathe through the disorganised Roman lines. Panic welled up and swept ahead of the British onslaught and some legionaries backed away, while others simply turned and ran to the right of the line.

'Dear gods,' said Sabinus. 'They're trying to drive us into the marsh.'

'And they'll do it,' said Vespasian grimly, 'unless we intervene.'

'Us?' Sabinus looked horrified. 'What can we do? We should guard the camp, so the survivors have somewhere to run.'

'Survivors? There won't be any survivors. They'll run all right, straight into the marsh and drown, or be stuck in the mire and cut to pieces,' Vespasian reached over and gripped his brother's arm. 'Sabinus. it's down to us. There's no one else. Do you understand me?'

Sabinus recovered his self-control and nodded.

'Good!' Vespasian released his arm. 'Now go into the camp and fetch the other four cohorts and any auxiliary troops you can find. Get them formed up as quickly as you can and attack straight down the hill. Make as much noise as you can. Now go!'

'What about you?'

'I'll take my chances with what I've got here.'

Sabinus wheeled his horse and spurred it up towards the main gate the camp, bent low across the beast's neck as he kicked his heels in.

With a last glance after his brother, Vespasian wondered if they would ever meet again in this world. Then he pushed the grim thought from his mind, and steeled himself for what he must do if the army and his Emperor were to be saved. He turned to his tribunes and called them over. The young men listened intently as he delivered his instructions as crisply as he could and then galloped away to deliver the orders to the senior centurions of the six cohorts. Vespasian dismounted, handed the reins to a a groom and asked for his shield to be brought to him. He undid the clasp on his scarlet cloak and let it slip to the ground.

'Make sure that is taken back to my tent. I'll need it tonight if it gets cold.'

'Yes, sir.' His personal slave nodded with a smile. "I"ll see you later then, master.'

Having checked the chin strap of his helmet and made sure that his shield grip was dry, Vespasian drew his sword and rapped it on the rim of his shield. He glanced over his cohorts to make sure that all was ready. The men were standing to, silently formed up and intently following the action down in the vale as they waited for the order.

'The Second will advance, on the oblique!' he shouted out, and the order was quickly relayed along the line. He counted three before the execution phase of the order and then filled his lungs. 'Advance!'

At a steady pace the six cohorts moved forward and started down the slope towards the shouts and screams of the desperate battle being fought in the vale. The mist was rapidly thinning and starting to reveal the full scale of the disaster facing Claudius and the other three legions. Caught out of formation and sent reeling by the surprise attack from the forest, the rear ranks had broken and were blindly fleeing across the battlefield towards the marsh. Scattered pockets of resistance showed where a centurion had managed to show sufficient resolve and presence of mind to gather men to face the British pikemen. Ranged behind their closely aligned shields, small groups of legionaries fought their way towards each other but they were getting the worst of it because of the reach of the enemy's pikes.

The standards of the Fourth Cohort bobbed up and down with the rhythmic pace of their bearers and Cato's eyes were automatically drawn to them as their gilded decorations caught the sun and glowed with a fiery burnish. The cohorts were marching in two lines of three centuries, with the Sixth Century positioned on the right of the rear rank. Cato had a clear view of the line of advance. The tall oaks of the forest loomed up ahead and to the left of the Second Legion, wide trails leading into their shadows clearly visible now that the briar screens had been discarded. Ahead and to the right bodies were strewn across the trampled grass, which was still wet with dew that drenched his boots. The cohort passed over the remains of the left flank artillery battery. Most of the weapons had been knocked over, and the bodies of their crews lay crumpled all around. Cato had to sidestep the corpse of a centurion, and glancing down he felt the bile rise in his throat at the sight of the bloody gristle and severed tendons in the side of the officer's neck where a sword blow had nearly taken his head off.

They kept on moving and left the carnage of the battery behind. As they advanced, Cato saw that at last some of the enemy were responding to the cohorts' approach. The nearest of the pikemen had turned to face the threat and were shouting warnings to their comrades. More and more of them turned to attack the Second Legion, screaming their war cries as they levelled their pikes.

'Halt:' Vespasian bellowed.

The cohorts drew up one pace on, hands tightening round their javelins in anticipation of the next order.

'Prepare javelins!'

The legionaries of the front line of centuries hefted the shafts of their javelins and stretched their throwing arms back. The British charge faltered. With no shields to protect them, the pikemen well knew how vulnerable they were to a volley of javelins.

'Release!'

The legionaries' arms flew forwards, releasing a ragged belt of dark lines that arced up in the air towards the Britons. As they reached the highest point of their trajectory the javelins seemed to hang for an instant, and the war cries of the Britons abruptly died in their throats as they braced themselves for the impact. The tips of the javelins dropped, and the volley plunged down into the British ranks, tearing into and through the unprotected bodies of the pikemen. The charge collapsed at once and the Britons who survived the first volley glanced fearfully towards the cohorts as Vespasian called the second line to readiness. But there was no need for another shower of javelins. Almost as one, the Britons backed away, not willing to brave another volley and join their stricken comrades lying dead and wounded amongst the jagged hedge of javelin shafts whose heads had buried themselves in bare flesh and soil.