The light armed cohorts discussion and evidence

[jkaler48]

I am thinking the possibly lead weighted Pila are heavy Pila and may also have been used primarily as a fortified position defensive weapon being difficult to throw back UP at the defenders.
"caes.gal.7.82": [7.82] While the Gauls were at a distance from the fortification, they did more execution, owing to the immense number of their weapons: after they came nearer, they either unawares empaled themselves on the spurs, or were pierced by the mural darts from the ramparts and towers, and thus perished. After receiving many wounds on all sides, and having forced no part of the works, when day drew nigh, fearing lest they should be surrounded by a sally made from the higher camp on the exposed flank, they retreated to their countrymen. But those within, while they bring forward those things which had been prepared by Vercingetorix for a sally, fill up the nearest trenches; having delayed a long time in executing these movements, they learned the retreat of their countrymen before they drew nigh to the fortifications. Thus they returned to the town without accomplishing their object.