The Viking era is usually said to be roughly from 793 AD to 1066 AD, ie from the first Viking raid on the monastery at Lindisfarne to the Battle of Stamford Bridge when the last Viking king, Harald Hardraada, lost his bid for the English throne. When I first started writing this series, I knew I couldn’t cover all that time and I had to decide which parts to base my stories on. So I made a chart of all the events that were known to have happened from 750 AD onwards, and discovered that the years between 850 and 900 AD were jam-packed with possibilities. At that time, the Swedes were heading east and south down the Russian rivers, the Danes (and others) were raiding and conquering in Britain and Europe, the Norwegians established a kingdom in Ireland and started settling on Iceland, and there were internal power struggles in Scandinavia too. This gave me a rich historical tapestry from which to choose events that my characters could be part of.