Prehistory means any time before recorded history - which is generally before the Romans arrived - so in Essex this covers the period 500,000-43 AD. Prehistory is normally divided into three periods, based on the material of the tools that have survived from these times:
Prehistory is a very interesting period, because it is during this time that people move from a lifestyle based on hunting animals and fish, and gathering wild plant food, to one based on settled farming of crops and animals, and also because it covers most of the human past. Surviving prehistoric monuments like Stonehenge retain an air of mystery about them.
About 472,000 years ago, at the beginning of what geologists call the Anglian stage of the Ice Age, an ice sheet covered most of Essex. When this ice sheet reached Essex, the Thames was flowing through the Vale of St. Albans towards Colchester. A lobe of ice blocked the river and it was diverted towards its present course.