The toponymy of England derives from a variety of linguistic origins. Many English toponyms have been corrupted and broken down over the years, due to language changes which have caused the original meanings to be lost. In some cases, words used in these place-names are derived from languages that are extinct, and of which there are no known definitions. Place-names may also be compounds composed of elements derived from two or more languages from different periods. The majority of the toponyms predate the radical changes in the English language triggered by the Norman Conquest, and some Celtic names even predate the arrival of the Anglo-Saxons in the first millennium AD.