Figure 29 is a schematic drawing of the cross section of a cathedral with a flying buttress support system. The construction parts of the drawing are coloured in pale brown to emphasize the existence of clear air between the buttress system and the main building. The main building is in the centre of the drawing and comprises a very tall and narrow central nave that reaches to the top of the drawing supported on either side at the bottom by lower halls with church style entrances to signify that this is a section of a cathedral. These lower halls appear to support the bottom third of the nave walls. This representation of the main building has been drawn using thick darker brown outlines to distinguish it from the supporting buttress system. The buttress system is on the outside of the main building and is drawn using thin black outlines. This drawing is a cross-section and so only shows one buttress system on either side of the main building. These systems are mirror images of each other. The structure of the buttress system is based on a solid tower, which is widest at the bottom and reduces in two step changes to a thin pointed section whose tip is nearly at the same height as the roof of the nave. The thickest lower third of the buttress tower is the same height as the outer halls of the main building. A solid arch then crosses from the buttress tower through the air above the outer hall to attach to the wall of the nave at about two-thirds the way up. The second section of the buttress tower also ends at about two-thirds of the height of the nave. Another solid arch then crosses from the buttress tower through the air above the first lower arch to attach to the top of the nave. These two arches are the flying buttresses. The buttress tower then has a final smaller section which is capped with a miniature pointed spire.