The name Essex derives from the Kingdom of Essex or Kingdom of the East Seaxe which was traditionally founded by Aescwine in 527 AD, occupying territory to the north of the River Thames and east of the River Lea.
In 825 AD it became part of the Kingdom of Wessex and was later ceded under the Treaty of Wedmore to the Danelaw control of the Kingdom of East Anglia. In 991 AD the Battle of Maldon resulted in complete defeat for the Anglo-Saxons against the Vikings and led to the poem The Battle of Maldon.
The area which Essex now occupies was ruled pre-Roman settlement by the Celtic Trinovantes tribe. A dispute between them and another tribe was used as an excuse for a Roman invasion in 55 BC, and they allied with Rome when Claudius returned in 49 AD. This led to Camulodunum (Colchester) transferring from the Trinovantes to the Roman Empire as the capital of Roman Britain. The Trinovantes later fought with the Iceni tribe against Roman rule as the Romans did not accept that in the Iceni tradition women could be rulers and therefore after Boudicca became ruler they sought to take power which was not part of the agreement that they had come to.
The county has lots of Bronze Age, Iron Age, Roman, Saxon, Viking and Medieval activity in this area.
For more history of the county of Essex please click here - http://www.visitessex.com/discover/historic/