There's a great map at the Sutton Hoo site in Suffolk with the times to reach other places from there. Measured in days. It shows an empire based around the r

There's a great map at the Sutton Hoo site in Suffolk with the times to reach other places from there. Measured in days. It shows an empire based around the rim of the North Sea and you can immediately see why when you compare the times to reach anywhere over land compared to the see.