In classical art, however, only slaves, barbarians, and a scattering of mythological figures were shown with large penises.
The artistic ideal was always the adolescent athlete, represented as he would look during or just after hard exercise. A vigorous workout—and especially a vigorous workout vigorously conducted in the nude—causes the penis and testicles to retract. After a long run or wrestling match, a nude athlete’s genitals would be diminished appreciably. This fact doubtless helped to establish the artistic convention.
Above all, a diminutive and pointedly unpointed penis advertised self-control.