Assuming Jesus was a real person, it is a generally accepted fact that he died on a cross. On the other hand, Jehovah's Witnesses are of the belief that the crucifixion of Jesus is a mistranslation and the word stauros shall be translated as "pole", not "cross".
But now there's seems to be some academic support for the pole interpretation. According to a doctoral thesis by Gunnar Samuelsson at the University of Gothenburg, there is actually no mention of a cross in the original or contemporary texts.
From the press release:
The thesis clearly shows that although the studied texts are full of references to suspension of objects and the equipment used to this end, no reference is made to 'crosses' or 'crucifixion'. Samuelsson therefore concludes that the predominant account of the destiny of Jesus is not based on the antique texts, but rather on for example the tradition of the Christian church and artistic illustrations.
From the Telegraph:
He claims the Bible has been misinterpreted as there are no explicit references the use of nails or to crucifixion - only that Jesus bore a "staurus" towards Calvary which is not necessarily a cross but can also mean a "pole".
From the Atlantic Wire (my emphasis):
Samuelsson did some serious research before advancing this provocative argument: "I spent almost three years," he says, "reading all the ancient texts I could find ... from about Homer until the first century of the Common Era." He says "some kind of suspension of a living or a dead person or a part of a person" was indeed common at the time, but crucifixion is not mentioned. In the Bible itself, all it says is that Jesus carried and then was executed on a staurus--"there is no other description beyond that."
Specifically, are there really no original sources that explicitly mention the practice of crucifixion in the sense generally understood today?