In those times, most would be happy a wall looked straight, and vertical enough to not fall. Also, a circular wooden object (a spool, wagon wheels, ...) could h

In those times, most would be happy a wall looked straight, and vertical enough to not fall. Also, a circular wooden object (a spool, wagon wheels, ...) could help to maintain the forms. The Dutch Wikipedia mentions many variants formed from straight segments. Probably the labor cost would have been about the same, and workers happier because of the variation involved.