Here's what you need to know about the timing: the show is both radically compressing and extending eras. For instance, in season one, Ragnar and his crew raid the monastery on the coast, which is probably representative of the famous "Sack of Lindisfarne" that took place in 793 AD. But if you fast-forward to season three, the "Siege of Paris" plot line mimics events that took place in 911 AD. That's over a century's worth of action jammed into just a few short years, probably to touch on all the historical highlights.
But Dr. Godlove has predictions, like any fan would. She predicts that Vikings' writers are setting up Rollo (our favorite shirtless warrior) to be the Rollo of medieval lore "who struck a deal with the Frankish King Charles the Simple, that allowed him to settle in the Northwestern territories of Francia." (France to us laymen.)
This means the story line with Rollo and Gisla (which means "hostage," oddly enough) is destined to join up for season four. We saw that look he and the princess exchange. We've been shipping them ever since.
