Depictions show that the upright and the cross beam are square in width and depth and perfectly flat. How could they get them that way back then? Did they have saws? Mills? They would have had axes.
They show the crossbeam as intersecting the upright. But how could it? It would have to rest upon the upright. Some pictures show it tied to the upright by rope. How solid would that be? It would tilt. I opt for one upright because it is easier.