 Complete the following phrase:  Velites did not form their own units; a number of them were attached to each maniple of hastati, principes and triarii. They were typically used as a screening force, driving off enemy skirmishers and disrupting enemy formations with javelin throws before retiring behind the lines to allow the heavier-armed hastati to attack. They were normally the ones who engaged war elephants and chariots if they were present on the field, such as in the 