The Anglo-Saxons are believed to originate from three tribes of Germanic peoples who occupied what is now Denmark and part of the costal areas around this peninsula. Angles, Jutes, and Saxons are the names. It is thought that they had already established trade relationships with the Britons and had for many years prior to our Vortigern been in contact with the island. When the Picts arrived from the north, and the Irish (Scotti) from the west, they were part of the defense of the island. The Anglo-Saxon historians, writting some 400 years after Gildas around 900 AD, write the events this way:
446. The British sent men over the sea to Rome, and asked help against the Picts, but they never had it, because they were on an expedition against king Attila the Hun. They sent then to the Angles, and the Anglian athelings, with the same request.
449. ...In their days the Anngles were invited here by king Vortigern, And they then came to Britain in three longships, landing at Ebbesfleet. King Vortigern gave then territory in the southeast of this land, on the condition that they fight the Picts. This they did, and had victory wherever they went. They then sent to Angel, commanded more aid, and commanded that they should be told of the Britons' worthlessness, and the choice nature fo the land. They soon sent hither a greater host to help the others. Then came the men of three Germanic tribes: Old Saxons; Angles and Jutes...First of all, they killed and drove away the king's enemies: then later they turned on the king and the British, destroying through fire and the sword's edge.
455. Hengest and Horsa fought Vortigern the king, in the place called Aegelesthrep his brother Horsa was killed, and after that Hengest and his son Aesc received the kingdom.
456. Hengest and Aesc fought the Britons in the place called Crecganford. There they killed four companies. The Britons gave up Kent. and in great fear fled to London.
465. Hegest and Aesc foought the Wesh near Wippedesfleot and killed twelve Welsh ealdormen. One of their own thanes was killed there, whose name was Wipped.
473. Hengest and Aesc fought the Welsh and seized countless spoils of war. The Welsh fled the English as one flees fire.
The above was taken from: The Anglo-Saxon Chronicles, translated and collated by, Anne Savage, Crescent Books, New York, 1995, p. 29.