Former discrete English county, now divided into EastSussex, with its administrative headquarters at Lewes, and West Sussex with its administrative headquarters at Chichester. It was also a medieval Anglo-Saxonkingdom, traditionally founded by the Saxon king Aellein the late fifth century a.d. Defeating the Romano-British, the kingdom remained independent until subject at various times to Kent and Mercia in the sixthand seventh centuries. Conquered in 771 by Offa of Mercia, it remained under Mercia until Egbert of Wessexbrought it under his sway in 825. In 1066 William the Conqueror landed here at Pevensey and defeated King Harold of England at Hastings. The area has numerous prehistoric remains and Iron Age hill-forts.