It was almost midnight when the first move was made. By now the moon was well up, and providing enough light that troops could move slowly and quietly, but not that bright that the enemy would see them other than by carefully searching. He had left a small squad of auxiliaries at the first gully out in the desert, with orders to conceal themselves, allow the Parthians to advance on the oasis, and then follow up from the rear. They had clear instructions of what to do on the first night of the Parthians setting up camp. As Gaius reflected later, had the Parthians not set up camp, but attacked directly as Alexander did on more than one occasion, these orders would have been wasted.
In the light of a three-quarter moon these men now advanced carefully on foot towards the baggage camp. The Parthians were keeping a poor watch, most of it directed at the Roman camp, and the auxiliaries reached the baggage camp unobserved. There appeared to be only three guards, and these were close together, and engaged in some sort of conversation. The auxiliaries quietly dispatched the three guards. Then the easily found water containers were punctured and the horses were untethered. The auxiliaries then advanced to the nearest fire, and lit torches. A signal was sent to the few left behind to quietly bring their own horses up.
What fires that could be lit were lit amongst the baggage, then the Parthian fodder was put to the torch and the horses released. As the fires started, the raiders mounted the spare horses brought up from the rear, grabbed torches, rode into the camp and lit whatever further fires they could, then turned and, using the torches, made sure the enemy horses were in full flight.
As the alarm was raised, the cavalry from the oasis attacked. With the Parthians running hither and thither, half asleep, unprepared, for it was common knowledge that Romans did not attack at night, they were easy prey for the cavalry. Many tents were put on fire and up to a hundred Parthians fell to the lances before any organized defence could begin. Then, as the Parthians began to gather arms and form small lines, the Roman cavalry rode around them, slashing with their swords and riding through to attack another group from the rear. Then, when the Parthians finally became organized, the cavalry noisily rode back to their camp. Less obviously, the first small detachment rode quietly and apparently unnoticed back towards the desert.
From Gaius' point of view, the raid was a huge success. The enemy had sustained significant casualties, much of their cavalry had been neutralized, and they were now forced to fight their way to water. Any attempt to send for help should be intercepted by the desert squad.
At dawn, Gaius surveyed the field. The Parthians were gradually assembling into formations. The Roman camp was buzzing. Food was prepared, the soldiers were checking equipment, and although everything seemed disorganized Gaius knew that very little time would pass between the Centurion's command and the forming of battle lines.
The order for battle was set. The archers were divided equally and placed at the centres of the two hillocks, the largest centuries, each with about ninety men, were placed two per hillock, three centuries defended behind the sides of the hillocks, while the cavalry was kept to the rear with the remaining men and auxiliaries, split into three 'centuries', as reserves. The ballistae he had were set up at positions where their huge arrows would tear into forces on the narrow flat ground between the hills should the enemy attempt to come through there. A catapult was mounted on the top of each hillock, where huge piles of suitable rocks were assembled. Signallers were in place. Gaius first rode around each century, ensuring that each Centurion now had a clear idea of how he intended to fight this battle, and what would be required of them then he rode to the top of the right hand hill to survey the scene.
Much of the morning passed while little happened. The Parthians drew up in formation over a mile away, but then did nothing. They stood there, as if challenging the Romans to advance. The sun became hotter and hotter, and the flies became more irritating. Some Parthian insults could be discerned over the distance. Gaius issued his first order. In turn, two thirds of his men could rest in shade specially erected.
A small group of Parthian cavalry rode towards the Romans, suggesting that the Romans surrender, and when there was no favourable response, they began hurling insults. Gaius had anticipated this. The soldiers at the top of the hillocks stood tall, and began pouring water over themselves from large jugs. They had the luxury of being able to cool off; they had the luxury of plenty of water.
Gaius sent the message for the Parthians to lay down their arms and surrender. The Parthians would become Roman prisoners, but at least they would drink. If they surrendered now, or any time before one Roman soldier was killed, he promised to spare their lives.
It was noon when the standoff ended. It was clear to the Parthians that the Romans were quite happy to sit tight, and it was equally clear that water was in short supply. Time did not favour the Parthians. When the Parthians began to assemble what was left of their cavalry, Gaius decided to ride back to the reserves. He realized that where he was placing himself was the weakest part of this deployment. If he wanted to see, he had to stay on top of a hill, but then he also had to hope the Parthians did not try to outflank the other hill. If he wanted to properly control the reserves, he had to be at the rear, with them. He had to hope that his men on the hills would inform him of the enemy's deployment.
The initial attack was a cavalry charge, directed at the gap between the two hillocks. As the earthworks slowed the horses down, the archers and the legionary slings clinically cut riders down. As more of the cavalry charged into the gap, the passage became congested, and at this point the ballistae let fly. The huge bolts soared through the air, to crash into the concentration of horsemen. Then as those at the front began to realize that too few of them could emerge from the pass at any given time to force the issue, they turned and tried to retreat. As the leaders were trying to return, the rear was still charging forwards, and the bodies began to pile up in the centre as more and more giant arrows broke bone after bone.
Gradually the situation became clear, and what little was left of the cavalry began a general retreat. Gaius ordered the auxiliaries to go forward, recover what arrows they could, particularly those suitable for the ballistae, and also save uninjured horses. As the more badly injured horses were put out of their misery, moans from the remaining Parthians filled the air, and the flies could be seen gathering on the more badly injured. There was nothing that could be done for these men; his own forces needed to be ready to fight, and any impediment to the Parthian's progress had to stay there.
An hour later the Parthian infantry began to advance. The major column was clearly advancing towards the left hillock, with a minor column intent on forcing the issue to the left of that hill. Gaius signalled for one of the centuries defending the right side of the right hillock to advance towards the left hill and join those on the top, then he sent half his cavalry around through the gap on the extreme right.
Before this day, Gaius had no real idea of what war involved. He had had boyhood visions of glory; the reality, he soon found, was that it was a bloody mess. As the left flank of the advancing Parthians reached level with the base of the hillock, all they could see were the Roman archers on the hill to their left, and the remains of the cavalry charge. Horses were still twitching, men were groaning in the heat, men who were in pain, who knew they would die, and had to suffer while they were doing it. The advancing flank halted, unsure of what to do. They could hardly charge over their comrades, but the hillock climb would be congested. As they stood, a hail of arrows descended. The small shields offered some protection, but most men protected their face, and thus left their stomachs exposed. Some shields carried up to three arrows, but many of the men collapsed, groaning, desperately trying to tear the arrow out.