This is the first biography of one of the wealthiest and most influential bishops of medieval Europe, who for a period of over thirty years exercised a degree of power over the Plantagenet court second only to that of the king.

The career of Peter des Roches and the activities of his fellow aliens - examined here in detail for the first time - are fundamental to an understanding of the process by which England and France developed as two separate kingdoms. As a politician, des Roches cast a shadow across the reigns of both John and Henry III.

His biography encompasses the first detailed narrative yet attempted of English political history in the early 1230s and of the civil war of 1233-4: a period which, as the author argues, has been much misunderstood. In the process it sheds new light on such hotly debated issues as the role of aliens in English politics, the reception of Magna Carta, and loss of Normandy, and the constitutional and administrative developments of the reign of Henry III.