The Kingdom of Essex (Est Seaxna "East Saxons"), was one of the seven traditional kingdoms of the so-called Anglo-Saxon Heptarchy) was founded around 500 AD and covered the territory later occupied by the counties of Essex, Hertfordshire and Middlesex.
The kingdom was bounded to the north by the River Stour and Kingdom of East Anglia, to the south by the River Thames and Kent, to the east lay the North Sea and to the west Mercia. The earliest record of the kingdom dates to Bede's Historia ecclesiastica gentis Anglorum, which noted the arrival of Bishop (later Saint) Mellitus in London in 604. The territory included the remains of two provincial Roman capitals Colchester and London. For a brief period in the 8th century the kingdom also encompassed the Kentish Kingdom to the South, but by the mid 8th century much of the kingdom, including London, had fallen to Mercia. After the defeat of the Mercian king Beornwulf around 825 AD, the kingdom became a possession of the Wessex king Egbert. In 870 the territory was ceded by Wessex, under the Treaty of Wedmore, to the Danelaw kingdom of East Anglia. The modern Englishcounty of Essex maintains the historic northern and the southern borders, but only covers the territory east of the River Lee.
The dates, names and achievements, like those of most early rulers in the Heptarchy, remain conjectural. The dynasty claimed descent from the god Seaxn?at, rather than the god Woden (from whom the other Saxon tribes claimed descent). The list of kings may omit whole generations.
Sigered was the last king of Essex, and he ceded the kingdom to Egbert of Wessex.
Spelling of King's Names
There are a number of variations of the spelling of the names of the Kings listed above. This was a time when spellings varied widely, even within a document. Amongst these variations are the preference between þ and ð (unvoiced and voiced "th").
The character '7' was used as the ampersand '&' in contemporary Anglo-Saxon writings. The era pre-dates the emergence of forms of writing accepted today, notably minuscule, and the letters 'W' and 'U'. Where W was followed by U this was generally rendered as 'VV' (which was also used for 'W' alone).
Sources
Kings, Rulers and Statesmen, Clive Carpenter, Guinness Superlatives Ltd
Rulers and Governments of the World, Vol1, Earliest Times to 1491, Martha Ross