Premise: The Arabs captured Caesarea from the Byzantines in a.d. 639 and the Crusaders conquered the Arabs in 1101, discovering a green crystal vessel which they claimed to be the Holy Grail, the cup from which Jesus and his disciples drank during the Last Supper (it now reposes in Genoa).

Hypothesis: Caesarea was taken over by the Crusaders in a.d 647. 
Relation: contradiction