A county is generally a sub-unit of regional self-government within a sovereign jurisdiction. Originally, in continental Europe, a county was the land under the jurisdiction of a count. Counts are called earls in post-Celtic Britain and Ireland—the term is from Old Norse jarl and was introduced by the Vikings—but there is no correlation between counties and earldoms. Rather, county, from French comté, was simply used by the Normans after 1066 to replace the native English term scir ()—Modern English shire, as the Anglo-Saxon system of Shires was unique and thus hard for the Norman invaders to comprehend so they resorted to calling them Counties. A shire was an administrative division of an Anglo-Saxon kingdom (Wessex, Mercia, East Anglia, etc.), usually named after its administrative centre: for example, Gloucester, in Gloucestershire; Worcester, in Worcestershire; etc. Thus, whereas the word comté denoted a sovereign jurisdiction in the original French, the English county denotes a subdivision of a sovereign jurisdiction.