The 3D Cross
Several crosses appear to be designed as 3D; sometimes that is the intention, sometimes not. The Eastern Orthodox Cross, for example, where its lower slanting beam could be misinterpreted as an arm in a third dimension. Its similarity with a key is a convenient reminder that the cross is the key to forgiveness.
A further illusion is where there is no cross at all, as shown on the left. You may imagine a cross is there but actually there are only three black shapes, arranged in a certain position. (This style is popular tattoo design.)
The cross atop the canopy in the market square of Beverley, East Yorkshire (photo on the right) is deliberately three-dimensional. It can be recognised as a cross from any viewing angle.
Many town squares in Europe have a Market Cross. Beverley's dates from 1714, the latest renovation being in 2012 to celebrate the Queen's Diamond Jubilee.
(That six-armed cross looks uncannily like the car wheel brace I bought from Halfords, many years ago. I often wondered what happened to it.
Now I know.)
And finally our own designs (click any to enlarge), inspired by the Dutch artist M C Escher (1898-1972), Swedish artist Oscar Reutersvärd (1915-2002), and others, who had a passion for mathematically impossible designs.
Impossible for us, but Matt. 19:26 reminds us that "With God, all things are possible."