> Does anyone know when the Russian three bar cross came about?
A little browsing with Google turned up this site:
This is an abstract (with bibliograhy) of an academic paper on the history of the three-bar (a.k.a. Eastern or Russian) cross. Amongst other things it notes:
The Cross of St. Constantine, which resides within the monastery of Vatopedi on Mt. Athos, is a three-barred cross of the distinctly Orthodox design. This cross, hidden during the tenth century from Arab invaders and said by legend to be that of the monasterys original founder, predates the adoption of St. Andrew as the patron saint of Russia.
So that gives you an example from at least the 10th century; note that while Athos was predominantly Greek, it was certainly not exclusively so!
You might also want to have a look at:
This notes the initial adoption of the three-bar cross by the Kievan church.