The terms 'Bronze Age', 'Iron Age' and so on are used by archaeologists as a convenient shorthand for discussing the chronology of the past. In reality, the changes from one period to the next would have been far more gradual than these sharp distinctions imply. The accepted dates for these periods also vary in different parts of the world, because different areas developed at different times. Middle Eastern and Mediterranean civilisations, for example, developed metalworking before people living in Britain, so that their Bronze and Iron Ages arrived earlier.