elevating the nave
The early romanesque churches were very simple. A nave was covered by a barrel vault. Careful not to weaken the strength of it, windows were'nt created in the vault itself. But one had to take care of the strength of the walls to. This resulted in small and low churches with little and small windows.
By constructing two side aisles adjacent to the nave, one could enlarge the building without increasing the span. Supplementary theses aisles supported the main walls.
elevating the nave
The additional support by the side aisles allowed the builders to elevate the nave, creating more space. But this had its limits to. Look at the ext applet.
If the nave becomes too high, the side aisles lose their supporting role. A solution consisted in elevating the side aisles to by creating an additional tribune. This tribute hadn't got any functional role but supporting the walles of the building.
This technique was used in the church of Saint-Etienne in Nevers (late 11e century).
