The centre charged the hillock. They were running at the bottom, but by the time they had reached within thirty meters of the top, their charge had reduced to a walk. It was then the horn blew, and about a hundred and fifty pilii were launched. As the Parthians stared at this wall of javelins, and took what protection they could, the second volley was launched. Then, as the Parthians hid behind what cover their shields would give, the heavy crunching of Roman boots could be heard. The pilii tore into bodies, or pinned into shields where they bent, leaving a cumbersome and heavy object stuck at an awkward angle. A shield with such a pilum in it was almost useless, as it was impossible to wield quickly as the weight of the javelin had to be moved, and unless the shield was held high, the far end of the pilum would catch in the ground.
Then, as the second volley had landed, and those Parthians who were uninjured regained their feet, a wall of locked shields thrust into them. The Roman soldiers leaned forward on their shields, the weight of shield and man causing the Parthians to slip backwards, with some tripping and falling down the hill. As they slipped, the stabbing gladii tore into their stomachs, and as the wounded fell their skulls were trampled by the hob-nailed caligae as line after line of stabbing Romans walked over them. Then, as those in front began to fall back, they fell into their own men pushing forward. Although having overwhelming numerical superiority, the close fighting cancelled that advantage, and the sheer weight of men pouring downhill meant that the Parthians could not find the room they needed. Occasionally a wounded Parthian managed to fall with no pressure behind, which invariably lead to Roman soldiers falling forward, and becoming exposed, now to be cut down from the side. Parthian spears also entered between shields, killing or wounding Romans. The cries of pain of the wounded from both sides rose, and cries of pain began coming from the rear of the Parthian troops where the steady rain of ballistae bolts were taking their toll. Still the Parthians from the rear tried to advance, still the wounded piled up on the side of the hillock. The sun beat hotter, the flies buzzed more densely, the groans became more desperate. The charge began to falter.
On the Parthian right flank, the Parthians had more room to swing, and with their lighter armour, they were more mobile. Although Gaius had committed more troops here, he could not cover the entire gap. Suddenly, Gaius realized his mistake. The century that he had sent to the top of the hill should have joined those at the bottom. He ordered the horn to signal the left flank of his line there to wheel back.
As the Roman line wheeled, the Parthians there felt that victory was at hand. They attacked with renewed vigour, and they began to make some inroads. Yet when a Roman fell back wounded, his place was immediately taken from a soldier standing behind, and the line remained unbroken.
Gaius felt so helpless as he watched the line fall back and up-hill. He felt he should do something, but there was nothing he could do, other than to commit the last of his ballistae to firing into the midst of these Parthians. He still had reserves, but it was still far from clear where these should be deployed. The reserves were the last throw of the dice, and he wanted to send those to the point that would ensure victory, but the location of that point was yet to be determined.
The line began to retreat up the hill, and the Parthians advanced, only to find this was not a retreat. Gaius now ordered the next horn signal, and the Roman line, now two thirds of the way up the hill, stopped falling back. As the retreating line halted, and began steadier thrusting, the Parthians faltered, as if those at the front were unsure of what to do. They looked to their right, and the expected Parthian cavalry was nowhere to be seen, while from their left the sounds were those of Parthian agony, not the whoops of victory. They could not see what was happening elsewhere, but they could imagine. More than one of them began looking over their shoulders.
It was at that moment that Gaius realized victory was at hand. The enemy still grossly outnumbered his forces, they were better placed than they had ever been to force victory, but they had lost the initiative and they had lost their confidence. Now was the time to send a signal to the centuries on top of the right hill, which so far had been reduced to being spectators and to deploy his cavalry.
For a while the situation seemed static. The fresh centuries marched down the hill, while the cavalry that had flanked to the right were now stationary and level with the front of the right hillock. A signal was exchanged with the infantry, and the cavalry began its charge, to strike at the rear of the Parthians. The noise, and the unexpected activity from the rear caused a pause in the Parthian advance, then a wave of uncertainty passed over them. In a final attempt to gain the initiative, the leader of the Parthians ordered his right flank to advance, in one final attempt to get behind the hillock. Gaius now ordered his remaining centuries to march towards them, while he led his remaining mounted archers before them.
This final Parthian advance now found itself caught between two forces that, while admittedly small, could not be ignored. Gaius ordered the archers to fire, and he himself let loose arrows as fast as he could fire. Some of the Parthians peeled towards the cavalry, who pulled to their left, thus widening the Parthian front. It was then the Parthians found the last Roman century driving into them, thus splitting their line. It was then that Gaius remembered his analysis of the battle of Granicus. He picked out the Parthian leader, he aimed carefully at him and let loose two arrows, and was pleased to see his target fall towards the ground. He continued riding in and out, firing, until his supply of arrows was exhausted.
Now Gaius and the cavalrymen took their longer swords, and Gaius led a seemingly tentative charge towards the outer group of Parthians being divided by his century. He managed to get in two good blows onto two Parthians before it looked as if he would be overwhelmed. He wheeled his horse, and signalled for the cavalrymen to ride away. As they seemed to retreat, almost two hundred Parthians ran after them.
After he had ridden about a hundred and fifty meters, he ordered his horsemen to wheel. Now, the Parthians who had followed were strung out into a straggling line, and his horsemen charged at them.
As he told Timothy later, in some ways the charge was less effective than he hoped, as he spent almost as much effort trying to avoid falling off his horse as striking blows, but with the extended line of Parthians he could strike, regain balance, and strike again. In almost no time at all, these Parthians realized their position was hopeless and they began to run. Some ran back to their main force, but others simply ran. Some on the hill turned around, saw their fleeing comrades, and in the absence of clear orders, began to falter.
Gaius' small force now began to attack the Parthian flank. His tactics were 'hit and run' and his small force striking at different points increased the confusion in the enemy, as too many of them were spending too much time looking over their shoulders. These attacks were not free strikes, however. Four of his horsemen were pulled to the ground, and only two of these could make their escape. Gaius himself received a blow on his leg, which meant that later one greave, having done its job, had to be discarded, and he received a glancing blow to the other leg behind its greave, which meant that when he was on the next 'run' phase, he had to pause and tightly wrap his leg in a makeshift cloth bandage to stop the flow of blood.
As the final reserves of heavy infantry struck and this small force of cavalry seemed to move around their flank, the Parthians needed to know what to do next, and when they saw their leader down, the advance simply stopped. They tried to regroup into a square at the foot of the hillock, but the Roman infantry immediately closed on them, thus depriving them of the space they so badly needed. Then, to add to the confusion, large rocks flew into the centre of the Parthians from above.