The story of the Saxon invasion of England.
Saxons, along with Angles, Frisians and Jutes, invaded or migrated to the island of Britain around the time of the collapse of Roman authority in the west. Saxon raiders had been harassing the eastern and southern shores of Britannia for centuries before, prompting the construction of a string of coastal forts called the litora Saxonica or Saxon Shore, and many Saxons and other folk had been permitted to settle in these areas as farmers long before the end of Roman rule in Britannia. According to tradition, however, the Saxons and other tribes first entered Britain en masse as part of a deal to protect the Britons from the incursions of the Picts, Irish, and others. The story as reported in such sources as the Historia Brittonum and Gildas indicates that the British king Vortigern allowed the Germanic warlords Hengist and Horsa to settle their people on the Isle of Thanet in exchange for their service as mercenaries. Hengist manipulated Vortigern into granting more land and allowing for more settlers to come in, paving the way for the Germanic settlement of Britain.