As I remember there is a Pompeii graffito of a donkey being crucified,
scrawled on a wall by (obviously) a non-Christian with an attitude. I
think the cross was the standard one (Latin cross) but I'm not sure.
That's 79 A.D. evidence, but it could have been a misinformed opinion
I realize this has little to do with Greek, but while we're on the
subject, why does Paul refer to the cross as a tree? I don't have access
to the Greek word now, but maybe someone else knows. This had great
significance in Christian missionary tradition. For instance, the
Anglo-Saxons emphasized the tree (Dream of the Rood), and Scandinavian
religion already believed in a god who was hanged from a tree. But the
Anglo-Saxons also had a confusion of the cross with a GALLOWS & GIBBET, too.
The gibbet was T-shaped.