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.
Three dimensions also brings to mind the Holy Trinity.
Other illusionary 3-D crosses include the Dominican Cross (a form of Gyronny Cross), the logo of the Evangelical Lutheran Church of Brazil (ELCB), plus a few other church emblems.
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 for some people.)
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.
And finally one of our own designs, inspired by the Dutch artist M C Escher (1898-1972), who had a passion for mathematically impossible designs.
This impossible design reminds us of Matt. 19:26: "With God, all things are possible."