Just a note from L'Annee Philologique (the database for biblio in the classics):

Rebuffat René. - A propos des libritores. RPh 1988 LXII : 283-289. • L'examen des textes relatifs aux libritores permet de voir en ceux-ci des combattants généralement utilisés en compagnie des frondeurs, mais qui utilisent, au lieu de la fronde, une courroie en cuir. Ils sont identiques aux lithoboloi, et attestés depuis l'époque grecque classique jusqu'au début du ii s. ap. J.C.

Summary of an article by R. Rebuffat, in Revue de Philologie. To paraphrase (and summarise the article, which I've read)-- There's a smattering of references in Tacitus to people called the libritores, or libratores, who fight alongside the funditores, the slingers, shooting stones. (Don't have the references to hand, but it's the Annales and I think the Agricola). Now a mediaeval lexicon mentions them as well, and say they use an instrumentum bellicum involving leather, to throw stones.

Rebuffat thinks this is some kind of leather thong with which you throw stones, and that these libritores are the same as the lithoboloi, stone throwers, who are mentioned in Greek sources alongside slingers.

This latter point is probably wrong: these are just light armed hand throwers. It's also frankly unclear to my mind how a :leather stone throwing thong" is different from a sling.

T. Rihll may be right about these libritores: that they are some kind of crossbowmen with small stone throwing instruments. But it's pretty disputed.

FWIW

Very interesting. In a quick check, I see that they are mentioned as part of Germanicus' troops in the war against the Cherusci (A.D. 17/18 ?; Tac. ann. II,20) and of Corbulo's campaign against the Armenians and Tiridates (A.D. 57 ?; ann. XIII, 39). Unfortunately, I have almost no literature here that might be useful for a research >:(.

The Latin-German dictionaries on the internet are not more helpful than Rebuffat's suggestion, "one that throws stones with the help of a thong". Could mean anything from a leather sling to a bola (???) or stones tied to a thong.

As the word "libritor" seems to be related to "librator", somebody who weighs something with a scale or a balance (libra), couldn't a libritor be some (special) kind of fustibal user? Just a connotation off the top of my head...

I like that, actually-- the staff sling would look like a scales or balance.

Do you happen to know if Tacitus is the only source for the word? Or does it appear somewhere else so we might get another clue? The little information I squeezed out of the web only refers to Tacitus.

Hi Fundibularius-- I think it's just Tacitus + a mediaeval lexicon, but I must check to be sure ! But i like staff slings: the point about them is not that they shoot further, only heavier.