From the four-sided square, to the five-sided pentagon. Inside the pentagon is the pentagram. With a shape so like a human, arms outstretched, legs astride, this represents humanity. In early medieval symbolism the pentagram also represented the five wounds of Christ. The pentagon also brings us to the all-important Golden Ratio – so significant in sacred art, particularly from the Renaissance onwards. Just how ‘old’ the golden ratio is, is hotly disputed. Some historians say that Stonehenge, the Pyramid at Giza and – rather more likely – the Parthenon all show evidence of using this measurement, others suspect that to be a retrospective imposition. In the diagram shown here each line relates to every other: A is to B what B is to C and C is to D.