dome 6
The midpoints of the side of the basic square are connected by ribs. They create a second tier for a dome diagonally placed on the basic square.
In the four corners of the basic square little vaults sustain this second dome.
In the applet below you can see how such a configuration looks like in 3D.
![foto: [url=https://www.flickr.com/photos/100759833@N05/albums/72157649417564427]Santiago Lopez-Pastor[/url]](https://www.geogebra.org/resource/sa5kmyyc/Hfn3q0a3dcQZPEsd/material-sa5kmyyc.png)