Interesting factoid. I quote

To be sure, the body was foundational in the Greco-Roman construction of gender, insofar as Roman law required an infant’s classif i cation at birth as male or female. As one would expect, such classif i cation was done by visual observation of the external appearance of the genitalia.4Thus, initially the body did determine whether one was male or female. Still, once this classif i ca- tion was made, there was no guarantee that a given boy would grow to be- come a man. The problem was not just one of infant mortality, but whether the boy would live up to the requirements of masculinity. As Carlin A. Barton how to be a man in the greco-roman world17 puts it, ‘‘one was ontologically a male but existentially a man. Born a male (mas) or a human (homo), one made oneself a man (vir). A vir was not a natural being.’’5