This illustration, from 13th C France (called "God The Geometer"), appeared briefly during an episode of Nova that we were watching a few days ago. It was about how cathedrals were built - arches, buttresses, vaulted ceilings, etc..

That thing Jesus is measuring, doesn't it look like a free-hand rendering of a second-hand description of a mini-Mandelbrot or Julia set?

main()
{
   float C,l,c,o,O,I=-20;char _;for(;I++<20;puts(""))
   for(O=-46;O<14;putchar(_?42:32),O++)for(C=l=_=0;o
   =l*l,c=C*C,l=2*C*l+I/20,C=c-o+O/20,o+c<4&&++_;);
}