There are two Greek words used to describe the instrument of Jesus’ execution: xulon and stauros.
Neither of them specifically mean a cross.
Xulon just means a piece of wood. It may mean something as large as a tree trunk (e.g. the tree of life in Revelation is a xulon), or as small as a wooden club (e.g. the men who came to arrest Jesus were armed with xulon, or clubs). See Strong’s Concordance for more information.
Stauros just means a pole or a piece of lumber, but especially a pointed stake. This was the usage of other ancient Greek writers, including Homer, Herodotus, Thucydides, and Xenophon. See Strong’s Concordance for more information.
Translating these words as ‘cross’ is merely a tradition that appeared in later times. There is no description of a pole with a cross piece (making a cross) in any Bible manuscript.
Therefore, when it comes to Jesus’ execution, this translation uses ‘tree’ for xulon and ‘pole’ for stauros because that is what the manuscripts say. Also, staurotheto (which other Bibles translate as crucified) is shown as impaled (put on a pole or stake), because that’s what it actually means.
Are we saying that Jesus didn’t die on a cross? Not necessarily. There’s quite a bit of historical evidence to indicate that he likely did (see the Wikipedia entry, Instrument of Jesus’ crucifixion). The Romans used a variety of different shapes, and the cross-shape was frequently one of them.
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