Pythagoras was among the first Western thinkers to interpret life as a cycle of four phases, each roughly twenty years long and each associated with a season: the spring of childhood, the summer of youth, the harvest of midlife, and the winter of old age. The Romans likewise divided the biological saeculum into four phases: pueritia (childhood), iuventus (young adulthood), virilitas (maturity), and senectus (old age).
