'What the hell does he think he's doing?' asked Cato, astonished. 'They'll be cut to pieces.'

'They might buy just enough time for the rest.' Macro turned and looked back towards the ramparts of the depot. 'Where's the garrison?'

The distant thrum of hoofbeats and a thin defiant cry of 'Augusta!' announced the charge of the mounted scouts. Cato and Macro watched with sickening dread as the handful of horsemen swept over the sunlit grassland towards the screaming wave of Britons. For a moment the two sides were distinct forces, Roman against Briton, and then there was just a swirling chaos of men and horses, their war cries and screams of pain carrying clearly to those watching helplessly from the ramparts of Calleva. A handful of the mounted men broke free of the enemy and pelted back towards the wagons.

'Is the legate with 'em?' asked Macro.

'Yes.'

The sacrifice of the scouts only delayed their enemy for a short while, by which time the wagons and their escorting infantry were only two hundred paces from the gateway. Those on the wall shouted encouragement and wildly beckoned to them.

On came the Durotrigans, a seething mass of men and chariots, closing with their prey. The auxiliaries prepared to receive the charge. The dark slivers of the remaining javelins curved through the air and lanced down into the enemy. Cato saw one strike the head of a chariot horse and the animal reared up and spun to one side, dragging the chariot over and crushing its driver and spearman. The Britons swept past, unheeding, and threw themselves on the shields and swords of the auxiliaries, pushing them back on the retreating wagons.

Cato heard the steady tramp of marching boots from behind and turned to see the head of the garrison emerge from the heart of Calleva and march up to the gate. Below the wooden flooring of the gatehouse tower Cato heard the graunch of the heavy timbers of the gates as they were heaved open ahead of the legionaries.

'About bloody time!' Macro grumbled.

'You think they'll make a difference?'

Macro watched the desperate fighting engulfing the rear of the supply column and shrugged. The sight of the legionaries might just make the Britons pause in their onslaught. Over the last two years the natives had come to fear the men behind the crimson shields, and with good reason. However, these were the oldest of the veterans, lame men no longer able to keep up with their comrades, and those malingerers who could no longer be trusted to stand their ground in pitched battle. The instant the enemy realised the true calibre of the men they were facing all would be lost.

The first ranks of the garrison emerged from beneath the gatehouse. The centurion barked an order and the column changed formation, men spilling out on either side of the track to create a line four deep. As soon as the manoeuvre was complete the line moved forward towards the embattled supply column. The rearmost ranks of the Britons turned to face the new danger and slingers and archers loosed their missiles against the Romans. The barrage rattled harmlessly off the shields and then the noise ceased as the enemy infantry stepped forward to meet the legionaries. There was no wild charge from either side: the two lines simply came together in a rising clatter of ringing blades and dull thuds of shields. The legionaries pushed towards the first wagon, remorselessly carving a path through the Durotrigans.

The century continued to fight its way forward, but it was evident to those on the gatehouse that the pace was slackening. Even so, they reached the oxen of the first wagon and forced enough of a gap through the swirling ranks of the enemy to permit the wagon to drive through, rumbling free of the melee towards the open gates. The second and third wagons followed, and the surviving auxiliaries struggled to form up with their legionary companions. Vespasian dismounted and threw himself into the fight alongside his men. For a moment Cato felt a pang of anxiety as he lost sight of his legate; then the distinctive red crest atop Vespasian's helmet appeared amid the wild, shimmering mass of gleaming helmets and bloodied weapons.

Cato leaned over the palisade to watch the wagons pass beneath the gatehouse, each one laden with stacks of amphorae packed in straw. A small quantity of grain and oil would be saved, then. But that was all. As he looked up he saw that the last two wagons had fallen into British hands, their drivers and handlers lying slaughtered beside them. Only one last wagon was contested, and as Cato watched, the Britons began to drive the Romans back from it.

'Look there!' said Macro, pointing away from the melee. The British chieftain had gathered most of his chariots about him and was leading them wide round the fighting, clearly aiming to crash into the rear of the Roman line. 'If that lot catches them before they can reach the gate, the lads will break.'

'Break?' Cato snorted. 'They'll be cut to pieces… If only they see the danger in time.'

The Roman line was giving ground steadily under the weight of the Britons' attack. The men in the front rank thrust and blocked, wholly concerned with killing the enemy immediately to their front, while their comrades behind them were glancing nervously over their shoulders and edging back towards the safety of the gate. With a wild shout of triumph the charioteers suddenly whipped their ponies on, charging towards the narrow gap between the legionaries and the gatehouse. Even where he stood Cato could feel the walkway tremble beneath his feet as the ponies' hoofs and the chariot wheels shook the ground.

The centurion commanding the garrison glanced towards the chariots and bellowed a warning. At once the legionaries and auxiliaries broke away from their enemy and ran for the gateway, Vespasian amongst them. On the gatehouse Verica cupped his hands and shouted an order to the men lining the palisade. Throwing spears were snatched up and arrows notched to prepare a covering barrage for the fleeing Romans. Already they were streaming in through the gates, but some were not going to make it. The oldest soldiers, struggling pitifully with their heavy equipment, were falling behind. Most had cast their shields and swords aside and threw themselves on, glancing to their right as the chariots closed in, the manes of the ponies whipping out as their nostrils flared and their mouths foamed; above them the savage expressions of the drivers and the spearmen, exulting in the imminent destruction of the Romans.

Centurion Veranius, true to his kind, still carried his shield and sword, and trotted along with the last of his men, shouting at them to keep moving. When the chariots were no more than twenty paces from him he realised he was a dead man. Veranius stopped, turned towards the chariots and raised his shield, holding his sword level at his waist. As Cato watched, feeling sick in his guts, the centurion glanced up at the gatehouse and smiled grimly. He nodded a salute at the line of faces witnessing his final stand, and turned his face towards the enemy.

There was a scream, abruptly cut off as the chariots rode down the first of the stragglers, and Cato watched as the chain-mailed bodies of the legionaries were crushed to a pulp by hoofs and wheels. Veranius charged forward, stabbing his sword into the chest of a lead pony, then he was knocked down and disappeared under the confusion of harnessed horse-flesh and the wicker superstructures of the chariots.

With a grinding thud the gates were heaved back together and the locking bar crashed back into its receiving sockets. The chariots slewed to a halt in front of the gate and then the air was filled with shouts and shrill agonised whinnies as the javelins and arrows of Verica's men on the palisade rained on to the dense mass below. The Britons answered with their own missiles and a slingshot cracked against the palisade just below Cato. He grabbed Macro by the shoulder and drew him back towards the ladder leading down to the inside of the ramparts.