There are approximately 120 recorded Latin terms and metaphors for the penis, with the largest category treating the male member as an instrument of aggression, a weapon. This metaphorical tendency is exemplified by actual lead sling-bullets, which are sometimes inscribed with the image of a phallus, or messages that liken the target to a sexual conquest—for instance "I seek Octavian's asshole." The most common obscenity for the penis is "mentula", which Martial argues for in place of polite terms: his privileging of the word as time-honored Latin from the era of Numa may be compared to the unvarnished integrity of "four letter Anglo-Saxon words". Cicero does not use the word even when discussing the nature of obscene language in a letter to his friend Atticus; Catullus famously uses it as a pseudonym for the disreputable Mamurra, Julius Caesar's friend ("Dick" or "Peter" might be English equivalents). "Mentula" appears frequently in graffiti and the "Priapea", but while obscene the word was not inherently abusive or vituperative. "Verpa", by contrast, was "an emotive and highly offensive word" for the penis with its foreskin drawn back, as the result of an erection, excessive sexual activity, or circumcision. "Virga", as well as other words for "branch, rod, stake, beam", is a common metaphor, as is "vomer", "plough".