Crucifixion -- torture stake or cross? The Jehovah's Witnesses state that Jesus was not nailed on a cross, but on a torture stake. The New World Translation of the Bible is phrased accordingly. For example:

Matthew 10:38 (NWT)
And whoever does not accept his torture stake and follow after me is not worthy of me.

(All the other translations (that I know of) translate cross instead.)
What is significant about the difference between a torture stake and a cross, and on which one was Jesus crucified?

An illustration of what might be a torture stake:

Crux Simplex by Justus Lipsius (1547-1606). Wikimedia Commons.
There is comparatively little evidence in the NT for the shape of the object. There is not much etymological help from the Greek words σταυρός or ξύλον, which do not clearly indicate either shape.
Some of the textual hints we do have are:


  But [Thomas] said to them, “Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe.” (John 20:25, NIV)


This suggests that there was more than one nail placed through the hands, which is more likely on a cross than on a stake - though I could imagine a nail through each hand, with the hands side by side. But the JWs assert that the plural is referring to two nails, one through both hands and the other through both feet. The Greek reads "ἐν ταῖς χερσὶν αὐτοῦ τὸν τύπον τῶν ἥλων", which is "in his hands the imprint of the nails", clearly linking multiple nails to the hands specifically.


  Above his head they placed the written charge against him: THIS IS JESUS, THE KING OF THE  JEWS. (Matthew 27:37, NIV)


If Jesus were crucified as in the picture, the sign would be obscured by his arms. If it were also placed above his hands, Matthew could have written "Above his hands..." - but he didn't.


  Carrying his own cross, he went out to the place of the Skull, which in Aramaic is called Golgotha. (John 19:17, NIV)


Several different crucifixion methods were used by the Romans, including the traditional cross and the simple vertical stake. But the reference to carrying suggests that Jesus carried the crossbeam or patibulum of his cross - contemporary sources indicated that condemned people could be made to carry their own patibulum, but not the entire cross or stake, and of course a stake has no crossbeam at all. (Now-familiar depictions of Jesus carrying the whole cross come along later.)

It is common ground between Jehovah's Witnesses and the rest of us that for most of Christian history, Christ's crucifixion has almost always been regarded as being on a cross. The problem that the JWs have with it is that they think that the cross is a pagan symbol which was mistakenly (or maliciously) adopted early on in Christian history, as Christian belief and practice departed from its original form. As a restorationist group, they believe that in rejecting the cross shape they are returning to Christianity as it was meant to be. Insistence on the 'torture stake' is not particularly important in itself, but it is a prominent reminder of their distinctiveness, and of the error into which they think others have fallen.