Sacred Geometry
"The golden and Fibonacci ratios are fascinating ratios that can be represented as spirals, as rectangles, as number sequences and as 3D forms." Burrows, 3D Thinking in Design and Architecture, p. 141.
"The idea of ‘divine proportion’ stems from the mathematician Lucia Pacioli and his three-volume treatise De Divina proportione (1509), which was illustrated by Leonardo. The divine proportion was the golden ratio, or golden section (sectio aurea) as Leonardo called it. It was the ‘mean and extreme’ ratio of Euclid . . ." Burrows, 3D Thinking in Design and Architecture, p. 212.
"Pacioli’s ideas regarding proportion certainly influenced Renaissance artists, including Leonardo, but the De divina proportione itself is short of any new mathematical insights and construction methods, leaving readers in the dark as to how to develop the ratio in art and architecture. It is therefore highly debatable whether such artists actually used the golden ratio in any mathematically precise sense, but as an aesthetically satisfying visual proportion it is found in innumerable Renaissance works of art." Burrows, 3D Thinking in Design and Architecture, p. 212.

1 Note 1.
2 Note 2.