The Anglo-Saxons settled Celtic land and founded the state England there . . . .
So they weren't indigenous
to the British Isles . .
Like I said, they founded the first Germanic state on Celtic soil . .
They came from the area of today's Lower-Saxony and Denmark . .
This is why Frisian and English , to this day , sound similar . .
Going by that day's technique, it was quite something that they could settle an entire land going from coast to coast . .
After all , at that time there was no 'channel' present through which they might have taken a shortcut