Christianity

By ISO standard, the week starts on Monday. "Weekend" (週末) literally means "week's end," placing Saturday and Sunday last. Yet many countries start on Sunday—because in 321 CE, Constantine I made it a rest day, and "work then rest" felt more natural.

Medieval Europeans believed for centuries that "Prester John," a Christian king, ruled a powerful kingdom in Asia. This legend drove Prince Henry of Portugal to launch expeditions around Africa, helping catalyze the Age of Discovery.