A twitter rant (my first): stop translating the centurion rank primus pilus as "First Spear." This is a false etymology and makes a bad translation. Its seeped into popular culture (HBO's Rome, and elsewhere), but can also be found in academic press books. 1/

But it is wrong. Latin pilum does mean "javelin" but it is a very specific form, with an iron shank attached to a wooden haft. The generic Latin word for spear, both throwing and thrusting, is hasta. 2/

Now, the Primus Pilus was the first centurion of the last line of Roman heavy infantry, the triarii. Important note: the triarii did not until a very late date fight with pila (the plural of pilum). 3/

The triarii were the last line and bulwark of the legion. They fought with thrusting spears precisely because when "things came to the triarii"--a Latin saying--they needed a weapon one could stand and fight with, not one you threw away. 4/

So the pilum is not the origin of this centurions post. He and his soldiers were not armed with them, at least until the Late Republic. So where does the name come from? 5/

A lot of Latin words have the root "pil-". "Pila" means pillar or column; it can also mean mortar. "Pilum" in addition to heavy javelin, can mean pestle. The verb "pilare" means to ram, "pilatus," means "dense". And so on. 6/

All of these have related connotation of "mass that does something"; I won't go down the PIE rabbit hole. And here it is important to note that the triarii, the last line of the Roman legion, were once called the "pili" or "pilani" 7/

Again, nothing to do with pila, or javelins. Rather, it probably refers to the "mass" of heavy infantry---as in "column" in the military sense, or "bulwark" or even "phalanx." The name of these units changed over time to "triarii"--third liners. 8/

But the term "pilus" was enshrined in centurions ranks, which proved VERY conservative. So the commander of the first maniple of triarii is the "Primus pilus." He is the centurion elected first, and has a seat on the military council. 9/

So how to translate it? NOT "first spear!". Probably best translation might be "First Centurion" or "Chief Centurion." Or just use the Latin and call him "Primus pilus." 10/

And to complicate things, the genitive version of the title was common by the early Empire, so primipili, as in "centurion of the first pilus maniple." Rant over, I think 11/