The pila was adopted from the Etruscans and was originally called a "hasta longa"; I can't imagine why, as it was shorter than the 8-footer the triarii used.

Just to avoid confusion, the second lines were the "principes"; literally, the first, but this originally referred to their social position rather than their tactical one. The Romans had a long history, and some terms became "fossilized", and didn't keep up with contemporary practices.

Just my 2 bits.