Hasdrubal demurred, arguing that Carthaginian authority over the Iberian tribes was too fragile and the Roman forces in the area too strong for him to execute the planned movement. In 215 Hasdrubal eventually acted, besieging a pro-Roman town and offering battle at Dertosa, where he attempted to use his cavalry superiority to clear the flanks of the Roman army while enveloping their centre on both sides with his infantry. However, the Romans broke through the centre of the Carthaginian line and then defeated each wing separately, inflicting severe losses. It was no longer possible for Hasdrubal to reinforce Hannibal in Italy. The Carthaginians suffered a wave of defections of local Celtiberian tribes to Rome. The Roman commanders captured Saguntum in 212BC and in 211BC hired 20,000 Celtiberian mercenaries to reinforce their army. Observing that the Carthaginian forces in Iberia were divided into three armies which were deployed apart from each other, the Romans split their forces. This strategy resulted in two separate battles in 211, usually referred to jointly as the battle of the Upper Baetis. Both battles ended in complete defeat for the Romans, as Hasdrubal had bribed the Romans' mercenaries to desert. The Roman survivors retreated to their coastal stronghold north of the Ebro, from which the Carthaginians again failed to expel them. Claudius Nero brought over reinforcements in 210BC and stabilised the situation. Iberia, 211–205 BC In 210 BC Publius Cornelius Scipio, arrived in Iberia with further Roman reinforcements. In a carefully planned assault in 209BC he captured the lightly defended centre of Carthaginian power in Iberia, New Carthage, seizing a vast booty of gold, silver and siege artillery. He released the captured population and liberated the Iberian hostages held there by the Carthaginians, in an attempt to ensure the loyalty of their tribes. In the spring of 208BC Hasdrubal moved to engage Scipio at the battle of Baecula. The Carthaginians were defeated, but Hasdrubal was able to withdraw the majority of his army and prevent any Roman pursuit; most of his losses were among his Iberian allies. Scipio was not able to prevent Hasdrubal from leading his depleted army over the western passes of the Pyrenees into Gaul. In 207BC, after recruiting heavily in Gaul, Hasdrubal crossed the Alps into Italy in an attempt to join his brother, Hannibal, but was defeated before he could. In 206BC, at the battle of Ilipa, Scipio with 48,000 men,