"Then there was the great cross, which instead of the chest one touched his feet."
We still do this, generally in front of an icon. We make the sign of the cross and then bow low enought to touch the floor with our right hand fingers. This is called a metania and is generally done three times in succession. There is also the practice of full body prostrations which are made after making the sign of the cross. Generally it is done during Great lent when we pray the Prayer of +Ephraim the Syrian. We look like a bunch of Mohammedans and in fact it is from this ancient Christian practice that the Mohammedans got their method of prayer.
My new Son-in-law is new to this Catholic thing and the sign of the Cross is very strange to him. Since he is a high school baseball coach I have tried to expllain it as a signal from catcher to pitcher. He still isn't biting. He is just watching for now.
Dare I say that the practice comes from an older source: Judaism.
(By the way, I'd say you just sniped both Judaism and Islam, which knocks your "Closed Door" status off-scale low.)