Ali Reza Sverdalir sent me a drawing scheme for constructing arcs that are commonly used in Islamic Architecture.

when we use this combination of arcs in a 3D-model we get a configuration we can use in a circular dome as shown in the applet below:

But a photographs and plans clearly show the arcs aren't used to create a circular dome but placed in an octogonal one. This we will try to work out in the next activity.