Standoff at Ilerda
The Pompeian Defeat and Surrender
The battle of Ilerda (May-2 July 49 BC) was Caesar's first major military success during the Great Roman Civil War, and saw him defeat Pompey's most experienced armies, posted in Spain where Pompey had gained one of his earliest victories, against the forces of the Roman rebel Sertorius, and which had been his proconsular province in 55 BC.
Pompey's forces in Spain were commanded by L. Afranius, M. Petreius and M. Varro. Varro was posted in the west of Spain, leaving Caesar to face the combined forces of Afranius and Petreius, two experienced and capable commanders. The Pompeian commanders had the larger army, with five legions and eighty cohorts of locally raised troops, a total of around 67,000 men. Caesar had around 37,000 men, but his six legions were experienced and confident after years of victory in Gaul.
The city of Ilerda (modern Lerida in Spanish or Lleida in Catalan) sits on the west bank of the River Sicoris (modern Segre), just under twenty miles upstream from the point where it merged with the Cinga (Cinca). The combined rivers then flowed another five miles to join the Ebro. The city sat on one of the main roads of Roman Spain, which crossed the Sicoris on a sturdy stone bridge. The city itself sat above the west bank of the river on a significant hill. The terrain is hilly, becoming increasingly steep the further south one goes.
Standoff at Ilerda
Caesar sent an advance guard of three legions under his legate C. Fabius across the Pyrenees while he was delayed at Massilia. Fabius was able to fight his way past Afranius's forces in the mountain passes, and took up a position to the north of Ilerda. The river and the bridges across it would play a major part in the fighting that followed. Afranius and Petreius had control of the stone bridge at Ilerda, which gave them access to the land to the east of the river, and could use the river itself. Caesar relied on pontoon bridges built upstream from Ilerda, but these bridges were repeatedly swept away by spring floods.
The first indication that the bridges would cause problems came before Caesar reached the army. By this point Fabius appears to have received a fourth legion, and had built two bridges across the river, four miles apart. Every day part of his army crossed these bridges to forage for food on the eastern side of the Sicoris, having already used up all of the available food in the area between the Sicoris and the Cinga. One morning, just after two of his legions had crossed the river, the bridge they were using was swept away. The wreckage of the bridge floated by Ilerda, and Afranius decided to lead four of his legions and his cavalry across the stone bridge to attack Fabius's isolated two legions. Lucius Plancus, the commander of the two legions, took up a position on a nearby hill, where he was soon attacked. He was only saved by the arrival of Fabius's other two legions, which had crossed the other bridge.
Two days later Caesar arrived at Fabius's camp and took command. On the following day he decided to offer battle, forming up all of his legions in three lines in front of Afranius's camp. Afranius also formed up for battle, but he posted his lines on the hill of Gardeny. Caesar was unwilling to attack a stronger enemy up a hill, and instead decided to build a new camp where he was standing. While his first and second lines remained at arms, the men in the third line dug a fifteen-foot wide ditch behind them. By the time Afranius realised what was going on it was too late, and Caesar was able to camp within half-a-mile of the Pompeian position. Over the next few days the fortifications of the camp were completed.
This move put Caesar in a very strong position. The Pompeian forces were slightly spread out, with their camp on the hill half a mile outside Ilerda, but many of their supplies and a sizable garrison in Ilerda. Between the two strong positions was a flatter area, with a small hill in its middle. Caesar decided to try and seize this hill, fortify it and cut the Pompeian position in half. This attack did not go well. Caesar brought three legions out of his camp, one to capture the hill and the others to exploit their success. Afranius's men spotted the advancing troops just in time, reached the hill first and repulsed this first attack. The legion involved retreated, causing something of panic along the line. Caesar sent the 9th Legion to restore the situation, but they got carried away and were trapped under the walls of Ilerda, and were only able to retreat after a fight that lasted for five hours. Caesar reported losing 70 dead and 600 wounded in this battle, and admitted that both sides believed they had won.
Two days later the flood waters returned, and swept away both of Caesar's bridges. This left him trapped between the Segre and the Cinca, neither of which could be forded anywhere nearby. Supplies quickly ran short - the area had already been stripped of supplies by Afranius before Caesar's men first arrived, and anything that was left had already been eaten. Caesar was relying on supply convoys from Italy and Gaul, and these were now stuck on the wrong side of the river. Attempts to repair the bridges ended in failure, partly because of the high water levels and party because Afranius lined the opposite bank of the river with his dart throwers, who made it very dangerous for Caesar's men to work.
Afranius's control of the stone river bridge also allowed him to attack one of Caesar's supply convoys, which was trapped on the east bank of the river. The Gallic cavalry with the convoy managed to hold off Afranius's larger cavalry force for long enough for most men in the convoy to retreat to higher ground, but two hundred men were lost in the fighting and the price of supplies in the camp began to rise dramatically.
Ten days passed before Caesar was finally able to gain a foothold across the river. He ordered his men to use coracles, a form of boat that he had seen during his expeditions to Britain. The coracles were taken to a point 22 miles from his camp, a small force crossed the river, and took control of a nearby hill. They were able to hold this hill for long enough to allow a legion to cross the river, and then work began on a bridge. This was completed in two days, and the supplies were finally able to reach his camp. Caesar also took the chance to attack Afranius's foragers, sending most of his cavalry onto the east bank of the river, where they captured a large number of cattle.
The Pompeian Defeat and Surrender
This success meant that Caesar's supplies were now secure, but didn't break the deadlock. This he achieved through an impressive feat of engineering, digging a series of thirty-foot deep drains with which he intended to divert the course of the River Segre. This would have cut the Pompeian forces off from most of their supplies, and so Afranius and Petreius decided to abandon Ilerda and move their armies south of the Ebro, where they hoped to raise fresh troops. Work began on a bridge of boats at a town named by Caesar as Octogesa on the Ebro, and said to be about twenty miles from Ilerda. The exact location of this town is unknown, but it was probably somewhere downstream from the point where the Segre flowed into the Ebro. Afranius sent two legions across the Segre, and built a fortified camp opposition Ilerda.
There was a good chance that the Pompeian forces would escape safely. They still controlled the stone bridge at Ilerda, while Caesar's nearest bridge was twenty miles to the north. Work on the drains had lowered the water levels in the Segre to the point where the cavalry could ford the river, but the water still came up to the shoulders of the infantry. By the time Caesar's infantry had completed the forty mile round trip to the bridge, the Pompeians would have been safely across the Ebro.
Caesar sent his cavalry across the ford to harry the retreated Pompeians, while his infantry were forced to watch from the opposite bank. According to Caesar's account of the battle his infantry approached him and offered to try and ford the river. Caesar agreed, and with some care all but one of his legions was soon over the river.
Over the next few days the two armies manoeuvred around in the rough ground north of the Ebro, Afranius attempting to reach the river and Caesar attempting to gain control of the key valleys leading south. Caesar came out on top, and the Pompeians were soon trapped on high ground with no access to water. The campaign very nearly ended on the next day. Afranius and Petreius left their camp to supervise the construction of a line of fortifications to the nearest water, and while they were absent their soldiers came close to surrendering. Only Petreius's determination on his return to the camp saved the day, at least for the moment.
After a short time in this camp it was clear that the road to the Ebro was blocked. Afranius and Petreius had to choose between the road back to Ilerdia or an attempt to reach the coast. They chose to try and return to Ilerdia, but were harassed on every step by Caesar's men. Eventually they were forced to stop again, once again in a position without easy access to water. When Caesar began to build a line of his own fortifications around this new camp Afranius offered battle. Caesar formed his legions up into three lines, and was prepared to fight a defensive battle, but not to risk an attack. Neither was Afranius, and at the end of the day his men retreated into their camp.
Soon after this Afranius and Petreius requested a meeting with Caesar and asked for surrender terms. Caesar responded with a generous answer - their legions were to be disbanded while Afranius and Petreius were to leave Spain. Unsurprisingly the two men agreed to these terms. Those soldiers with lands or other possessions in Spain were allowed to leave immediately, while the rest would be escorted to the River Var. Afranius and Petreius themselves both made their way to join Pompey's main army in the Balkans, where they would continue to fight on against Caesar.
Caesar's victory at Ilerdia left one Pompeian army at large in Spain, that of Varro. He attempted to make a stand at Gades, but as Caesar advanced across Spain towards him his army dissolved, and eventually he submitted peacefully. The Pompeaen presence in Spain had been destroyed, at least for the moment, leaving Caesar free to return to Italy, before moving to the Balkans for the final showdown with Pompey.