The toponymy of England, like the English language itself, derives from various linguistic origins. Modern interpretations are apt to be inexact: many English toponyms have been corrupted and broken down over the years, due to changes in language and culture which have caused the original meaning to be lost. In some cases, words used in placenames are derived from languages that are extinct, and of which there are no extant known definitions; or placenames may be compounds between two or more languages from different periods. Many names 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.