Battle of Mercredesburne The Battle of Mercredesburne was one of three battles fought as part of the conquest of what became the Kingdom of Sussex in southern England . The battles were fought between the Saxon leader Ælle ' s army and the local Britons . The Anglo - Saxon Chronicle , states that Ælle arrived in Sussex with three ships and went on to fight at Cymenshore in AD 477 , Mercredesburne in 485 , and Pevensey in 491 . Ælle became the first king of the South Saxons . The Kingdom of Sussex was eventually annexed by the Kingdom of Wessex in the 9th century and went onto become the county of Sussex , England . Background . The legendary foundation of the Kingdom of the South Saxons is provided by the Anglo - Saxon Chronicle , that states that in the year 477 Ælle arrived at a place called Cymenshore with his three sons Cymen , Wlenking , and Cissa . The chronicle describes how on landing Ælle slew the local defenders and drove the remainder into the Forest of Andred and then goes on to describe Ælle ' s battle with the British in 485 near the bank of " Mercredesburne " , and his siege of Pevensey in 491 after which the inhabitants were massacred . The historian and archaeologist , Martin Welch suggests that the area between the Ouse and Cuckmere valleys in Sussex was ceded to the Anglo - Saxons by the British in a treaty settlement . Nennius , a 9th - century Welsh monk and chronicler , describes how the British leader Vortigern arranged to meet Hengest the Anglo - Saxon leader to work out a treaty . Vortigern and three hundred British leaders met with Hengest , supposedly to ratify the treaty , however Hengest ' s men slaughtered all of Vortigern ' s companions , after getting them drunk . Vortigern was then coerced into agreeing to a " treaty " that included the cession of Sussex to the Anglo - Saxons and the suggestion that " Mercredesburne " means " " river of the frontier agreed by treaty " " is seen as confirmation of this assertion . Battle . According to the Anglo - Saxon Chronicle of 485 , Ælle fought a battle with the British at Mercredesburne . Other versions of the battle have been derived from more elaborate descriptions , such as the one from Henry of Huntingdon , a 12th - century historian ' s version who suggests that when the army of Ælle and his sons engaged with the Britons neither side won and both sides pledged friendship although after the event the Anglo - Saxons sent a request to the German homelands for more troops . The 14th century chronicler Roger of Wendover even names the leader of the British forces as Aurelius Ambrosius . The problem for historians is that the Anglo - Saxon Chronicle was commissioned in the reign of Alfred the Great some four hundred years after the supposed events . There is some evidence that the Anglo - Saxons were using runes at this time . However their culture was largely of an oral tradition and they did not really start writing down legal and historical events until they were evangelised , this would have been the late 7th century for the South Saxons . The early Christian chroniclers would have taken most of their references for the early period from oral sources such as poetry . The medieval historians then produced embroidered versions of the chronicles to suit their own purposes . Aftermath . The Anglo - Saxon Chronicle does not provide any information on the death of Ælle or his succession , but Henry of Huntingdon suggests that Ælle died as the first king of Sussex in 515 and that he was succeeded by his son Cissa . Location . The location of the battle is unknown . The villages of Ashburnham and Penhurst in East Sussex maintain a tradition that a pre - Saxon earthwork known as Town Creep , situated in Creep Wood which adjoins the two villages , was the site of Mercredsburn . Oral tradition surviving to the end of the 19th century referred to the earthwork as being the site of a town which was besieged and destroyed by the Saxons . In 1896 members of The Sussex Archaeological Society investigated this claim , and subsequently published a paper concluding that the earthwork was a possible location for the battle of Mercredsburn , and that the modern name , Town Creep , could have an etymology derived from the latter part of ' Mercrede ' , whilst the ' burn ' ( or stream ) may refer to The Ashburn stream running beneath the earthwork .