Was it (stauros) a stake or cross?
I will cite a noted authority on this matter, "Judge" Joseph Rutherford who refers to this matter in his book of the 1920s, "The Harp of God". On page 135 of The Harp of God in a chapter titled “The Ransom”, Rutherford writes: “Thus died the Son of God, the great anti-typical ‘Lamb… which taketh away the sin of the world’. (John 1:29) In the eyes of those that stood by he died as a sinner, crucified between two thieves under the charge of disloyalty to the constituted powers, yet wholly innocent, harmless and without sin.”
On page 181 of the same book, on the first page of a chapter titled, String 7: Mystery Reveaedl, paragraph 299.
“ On the last night before his crucifixion [Jesus] was instructing them in various things that would be helpful to them in the days to come.”
As OGD wrote, Greek was the local language, but the administration of Palestine and court procedings were undertaken under Roman law. In an early episode of his career Julius Caesar crucified the pirates who took him captive among his many commentaries, if not on the Gallic Wars, but writing in Latin all the same. Spartacus and the other gladiators who had revolted in the 70s BC were crucified (6000, if not Spartacus included) by Crassus or Pompey, but the historical accounts (Appian and Livy) we have describe the administration of justice with the same Greek verb as appears in the NT. My conclusion: when a Roman writes stauros in Greek, he means cross.
I suppose much of this is a matter of the mind's eye. Substitute Christ saying to the rich man, give up all that he owns and "then pick up your torture stake and come follow me." Lenny Bruce had once considered the possibility of Christ's execution in New York state being by electric chair. ..But in either alternate case, somehow the message seems distorted. Cross in subsequent context signifies "sacrifice". I don't know about you, but to me, "taking up the torture stake" simply denotes masochism. Bad translation no matter how many crossbars are involved in one or the other.
The southern constellation Alpha Crucis is not simply a line but a cross...
If there were a transformation of this notion from stake to cross, it must have come early. Constantine's wife searched for the remains of the "true cross" and Constantine himself claimed he was inspired by a vision ("in hoc signum"). Whether either are inspiring or not, the vision of a vertical post does not seem as "visual" as two intersecting lines or timbers. Both of these 4th century figures spoke Greek; so I don't think they were having Greek translation problems. But they were not around when the "Judge" had a 20th century PR inspiration that would distinguish his movement from all of those millenia old "pagan cults". Just one of the many ways that Christian community had gone off the rails until the great leader, speaker and writer came along to put it back on the track after 1914.