Thania Ruiz the entire series is based in medieval times, easily found by looking up interviews on John Flanagan
Lily There isn't a specific date but I think the author said it is based in the medieval times. Especially since there are vikings
Pat The map in my copy, at the beginning of the Prologue, says "Year 643 Common Era" and appears to be loosely based on the geography of England and Scotland. Scandinavia comes into the story, too, in a fictional form, but overall, I'm reading it as a fantasy, not historical fiction.