Few knew and fewer cared to know about the boy's birth in a farmhouse in the tiny hamlet of Anchiano. The mother, an unwed rural girl, bore the oddly sentient child on a quiet Tuscan night in the spring of 1452 and then vanished into obscurity. Little more than her name, Caterina, has survived the centuries, part of the curious and marvelous legacy of her gifted son, Leonardo. Unlettered daughter of a nameless tenant farmer, vestige of medieval feudalism, she gave life to the most salient intellect of the Renaissance. What instincts or grace she imparted to him one cannot say. It is reasonable to believe, however, that she, as much as his notary father, Ser Piero di Antonio, was responsible for his naturally buoyant and restless spirit. Because of the circumstances, the boy was not given a patronymic or traditional family name. Instead, Ser Piero seems to have named him in honor of Saint Leo, a fifth-century pope venerated for his repulse of Attila the Hun and for his potent sermons. Leo's feast day happened to be celebrated during the week of Leonardo's birth.

Caterina probably nursed the infant for many months, because her social stature – and Leonardo's – would not have merited a wet nurse. Any joy shared between mother and child was short-lived, however. She soon relinquished him to Ser Piero, who, in the next year, married Albiera di Giovanni Amadori, a young lady of adequate public standing, and established a proper family. To mitigate the scandal of the illegitimate baby, Ser Piero's parents seem to have arranged, within a year of the birth, for Caterina to wed another peasant, a farmhand and kiln worker of good repute. Issues of love and compatibility never entered into such affairs. However, in accord with contemporary mores, Leonardo's honorable family would have provided her with a sufficient dowry.