Extract from the Anglo Saxon Chronicles 491AD
Original :- Her Ælle, Cissa ymbsæton Andredescester, ofslogon alle þa þe þærinne eardedon; ne wearþ þær forþon an Bret to lafe.
Translation :- Aelle and Cissa besieged Anderida , near Pevensey, and killed all who were inside, so there was not one Briton left.
Anderida is the Roman name for the Saxon Shore Fort at Pevensey, Andredescester means the fort at the edge of Andredesleage
(the forest now know as Andredsweald)
The South Saxons appear to have consolidated their western boundary at Chichester - the old Roman fortified city, and are now
working their way back to the East to ensure all 'Welsh' resistance is removed in the area south of Andredsweald.
From the distribution of places containing ing(nering - fortified) it would seem that they had consolidated the Adur valley then
followed the old Roman road north of the downs towards the east, pushing the 'Welsh' eastbound and finding resistance near Plumpton
and Barcombe/East Malling.
Then marching past Lewes towards Pevensey where they met further resistance at Wilmington, again near Polegate
where they trapped the remaining 'Welsh' on the small peninsular of Pevensey, finally attacking the Saxon Shore Fort of Anderida
present day Pevensey in which they killed all remaining there.
This is my interpretation of the village names, the Roman roads and the lay of the land but would seem to be a likely scenario.