In Season 2, episode 4 the vikings travel to Wessex. This is in late 700 AD. The main character Ragnar sees a bunch of excavated Greek/Roman statues and is told that nobody knows where they came from, and that the hypothesis is a former race of gaints once lived on the island.

Would the greeks really have built these monuments on the Island and if so would the "Saxons" really have no idea what these relics were at all? Why not?

In general I'm also interested in any inaccuracies put forward by the series and its reliability as a depiction of Viking life.

If this question dovetails into one of the FAQ's I apologize, I couldn't find it.