The golden ratio (roughly equal to 1.618) was known to Euclid.

The golden ratio has persistently been claimed in modern times to have been used in art and architecture by the ancients in Egypt, Greece and elsewhere, without reliable evidence golden ratio, also known as the golden section, golden mean, or divine proportion, in mathematics, the irrational number (1 + Square root of√5)/2, often denoted by the Greek letter ϕ or τ, which is approximately equal to 1.618.

It is the ratio of a line segment cut into two pieces of different lengths such that the ratio of the whole segment to that of the longer segment is equal to the ratio of the longer segment to the shorter segment.