Why gloucestershire is called gloucestershire?

Gloucestershire is named after the city of Gloucester, which was founded by the Romans in the 1st century AD. The name Gloucester is thought to derive from the Brittonic word *gloeucestri, meaning "bright fortress". The suffix "-shire" is derived from the Old English word scīr, meaning "a division of land". Thus, Gloucestershire simply means "the shire of Gloucester".