The Romans possessed a very sophisticated military apparatus from its organization to its tactical doctrine and equipment. One of the most common items a Roman legionnaire carried was the pilum. At a little over six feet long, with an iron tip set into a socket on the shaft the plum was a remarkably good throwing spear or javelin. One third of the pilum's length was dedicated to the iron shafted point or shank. The point was very heavy, more so than the socket end of the shank.
Some theories exist that the pilum bent upon contact, that the lighter socket end of the shank would not survive the throw. This would keep the enemy from pulling the weapon out and from throwing it back. Some theorize that the nails that connected the socket and shaft were made wooden to break easier.
The former has come under close scrutiny in recent years, and seem unlikely. The latter would make more sense as the weapon could be retrieved after the battle and set in a new shaft.
But the pilum, due to it weight in the shank, was a very deadly weapon, penetrating thick shields and armor.