Shropshire came into existence as a unit of government in the early 10th century. The oldest known form of the name of the county is SCROBBESCIRE, the shire belonging to SCROBBESBYRIG, the Saxon name for Shrewsbury. After the Norman Conquest the county's new rulers adopted the forms SALOPESCIRE and SALOPESBIRY. The word SALOP, applying both to the county and the county town, survived from the middle ages as an alternative English form, having originally been abbreviated from the Norman French. A Latin form, SALOPIA, was commonly used in documents in the 16th century, and in subsequent centuries legal records refer to the County of Salop rather than to Shropshire. The new authority established in 1974 under the Local Government Act of 1972 was officially named Salop, but this was altered to Shropshire with effect from 1st March 1980