This was formerly called the pilum, but now it is known by the name of spiculum.
From the en.wikipedia.org
The soldier carries a spiculum, a heavy pilum-type javelin.
From the en.wikipedia.org
Vegetius is writing about a one foot iron shaft because at Vegetius'time the pilum had disappeared and been replaced by similar shorter weapons such as the plumbatae or the above mentioned spiculum.
From the en.wikipedia.org
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Spicule: small pointed structure serving as a skeletal element in various marine and freshwater invertebrates e.g. sponges and corals
A spiculum is a late Roman spear that replaced the pilum at around AD 250 as the infantryman's main throwing javelin. Scholars suppose that it could have resulted from the gradual combination of the pilum and two German spears, the angon and the bebra. ...
A sharp, pointed crystal, especially of ice; A sharp, needle-like structure, especially those making up the skeleton of a sponge; A small radial emission of gas seen in the chromosphere and corona of the sun