The Romans moved to Phalanna (the capital of the Perrhaebi of northern Thessaly) for further harvesting. Perseus learnt that they were dispersed and no one was guarding the camp. He hurried with 1,000 cavalry and 2,000 Thracian and Cretan light infantry and caught the Romans by surprise. He captured nearly 1,000 carts and 600 men. Then he attacked a detachment of 800 Romans, which withdrew on a hill and formed a circle with interlocked shields as a protection against javelins. The Macedonians surrounded the hill, but could not make their way up. The Macedonians used cestrosphendons, a weapon which had just been invented. It was like a dart with feathers round the shaft shot by a sling held by two thongs. The slinger whirled it and it flew off. The Romans were getting tired and Perseus urged them to surrender. Pulbius Licinius was informed and he hurried with a force of light infantry and cavalry, including the Numidians and the elephants, followed by more troops.