sentences:  There is belief that the castle was built on the site of a 10th-century Danish Viking fort.This belief is because the Danish Vikings, who had landed in East Anglia in 865, participated in a battle at Tempsford in 921, on the possible location upon which Gannocks castle was later built, although this is conjectural.There is still some evidence of the castle, in the form of earthworks, and the moat still remains.