Treatise on the Laws and Customs of the Kingdom of England, c.1188. Attributed to Ranulph de Glanville (d. 1190), this is a text on English common law. Crucially, Glanville concentrated on decisions of justices as a basis for that law, i.e. on *jus, or on what had been done and decided in the past.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.