Sacred Geometry: A Primer

Ever hear of the Vesica Piscis? It's well, I'll show you first and then talk about it. You start with a line.

 Then you draw a circle on the line.

Then at the same compass setting draw another circle on one of the points where the circle and the line intersect.

That  area where the circles overlap is a Vesica Piscis, which I believe means something along the lines of "fish guts" you may recognize it as the 'Jesus fish' also Venn diagrams look like that. To learn more about the Vesica Piscis I refer you to Scread Geometry: Philosphy and Practice by Robert Lawlor, pages 32 - 35.
With the Vesica Piscis it's possible to create a double square, or other rectangle. To start, make another Vesica Piscis by drawing a circle on one of the points where line and circle intersect.
Draw lines between the verticals in the Vescias.

Connect between the lines.

This rectangle is not actually a double square but it is possible to make one this way.
 Or you can just make a cool design.