"Traditional rank amongst European royalty, peers, and nobility is rooted in Late Antiquity and the Middle Ages. Although they vary over time and among geographic regions (for example, one regionĀ“s prince might be equal to anotherĀ“s grand duke), the following is a reasonably comprehensive list that provides information on both general ranks and specific differences.[vague]" - (en.wikipedia.org 01.11.2019)
en