It was founded in the 6th century and covered the territory later occupied by the counties of Essex, Hertfordshire, Middlesex and (for a short while) Kent.
See asutati 6. sajandil ja kattis territooriumi, mille hiljem hõlmasid Essexi, Hertfordshire'i, Middlesexi ja (lühikeseks ajaks) Kenti krahvkonnad.