Pilum

Marius made modifications to one of the basic weapons of the Roman legionary -- the pilum.  Roman armies had been using the pilum for decades prior to Marius. Each soldier carried two. The pilum was essentially an infantry throwing spear, with a very small, wickedly barbed head of iron that continued as an iron shaft for about three feet.  This was joined to a shaped wooden stem which fit the hand comfortably. Roman practice was to wait until within 20-25 yards of an opponent then let the pila fly before closing to melee. In the past Roman armies had been bedeviled by the fact that these pila could be retrieved by an opponent and thrown back or otherwise be used against them.

Marius modified the pilum by introducing a weakness into the junction between the iron and wooden shaft sections. This was accomplished by replacing the one of the two iron rivets that joined the two pieces together with a wooden rivet. When the pilum lodged in shield, body or ground after being thrown, the wooden peg broke, making the pilum crooked, making it useless. Often the pilum became imbedded in an opponent's shield, making use of the shield difficult because of both the added weight and the awkward manner a shield with a spear embedded in it handles. Frequently enemy soldiers simply discarded the now useless shield -- making them easier prey for Roman sword play.

After the battle the pila would be recovered and the broken rivet would be replaced with a new one for use the next time.