In Appendices to its NWT, the WTS shows a picture from Justus Lipsius, in which a man is shown attached to a stake.
There is a number of pictures in the book by Lipsius, including a man being impaled. Following much enquiry, Lipsius decided that the implement was a cross as conventionally understood.
Pictures from the book by Lipsius are available at:
http://au.geocities.com/doug_mason1940/Pictures_from_Lipsius_de_Cruce_Liber_Primus.pdf
The picture of impalement is at the bottom LH corner of the second page.
Interestingly, Peter was told he would die with his arms outstretched, although tradition says he chose the upside-down position.
When the body of a crucified man was discovered, it was shown that the nails went through the wrists, his body contorted with feet on a rest. In his case, they ised the wood of an olive tree.
http://au.geocities.com/doug_mason1940/Aust_Inst_of_Archaeology_article_on_crucifixion.pdf
http://au.geocities.com/doug_mason1940/Archaeological_Evidence_for_Crucifixion.pdf
Doug