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.

-Greg Jordan