The rule of law tradition congealed into existence in a slow, unplanned manner that commenced in the Middle Ages, with no single source or starting point. Three contributing sources will be elaborated upon: the contest between kings and popes for supremacy, Germanic customary law, and the Magna Carta, which epitomized the effort of nobles to use law to impose restraints on sovereigns. Preliminary to considering these sources, a historical context will be laid.

By convention among historians, which is imprecise and by no means unanimous, the Medieval period of the West lasted for 1,000 years, commencing with the fifth-century collapse of the Roman Empire, terminating in the course of the Renaissance of the fifteenth and sixteenth centuries.

The first several centuries of this period are known as the Dark Ages. After Constantine shifted the capital of the Roman Empire to Constantinople, the western half of the Empire entered into a long decline precipitated by waves of invasions by Germanic tribes, who were unlearned barbarians by contrast to the refined Greco-Roman civilization they overran. The fearsome Huns, hitherto unknown Asian warriors originating from the distant east, mounted an invasion that thrust far into Europe in the fourth and early fifth centuries, driving the Germanic tribes (Goths, Visigoths, Ostrogoths, Vandals) before them in to the Roman Empire. Rome, sacked more than once, became a virtual backwater, with a fraction of its former population living amidst the ruins of the once great city.