THE BELLY

The viol's belly is traditionally built following two different methods, one by carving a thick board formed by joining two halves, the other one by gluing and then carving a number of wooden strips which are heat bent.
The number of the pieces varied usually from two (1) to nine.
In fact a third mixed method was sometimes used, which consisted in bending one or more strips, and carving the other thick ones. We can find historical instruments with the belly showing traces of bending, dating back to the late sixteen-hundreds.
It does not seem likely that this bending was done to save wood, rather to create a structure which could withstand the strings pressure. In this regard it makes sense to remember that a similar curved structure was already well known to the lute builders.

On the right you can see a part of the picture Sense of Hearing, of Jan Breugel (the Elder); the soundboard clearly shows the traces of the composite construction.
Click on the image to enlarge

Later on, the classic Northern Italian style prevailed, which provides that the belly be carved out of thick solid wood, but nevertheless viols were still often built with their belly made of 3 or more strips. The sound qualities typical of this building method were evidently preferred in certain musical styles.