The first voussoir, called the springer, although here identical in shape to the other voussoirs, is placed into the saddle.
The next time I visited my parents in Tucson, where my father had already accumulated a sizable rock garden in his back yard, I and my brother John scoured the grounds for rocks of approximately appropriate shape and constructed our own crude arch. Although it soon collapsed in a desert storm, our father was impressed with our creation.
In July of 2000, when we all came to say goodbye to Dad, I again enlisted John's assistance in making another crude arch of found stones outside of Dad's bedroom window. We first assembled this arch on the ground, using a propane barbecue tank as a form or scaffold, to hold everything in place until the keystone was inserted, and we were able to make it quite solid this time. Then we decided to elevate the structure on bases of two cinder blocks piled on either side. However, when we pulled the scaffolding out, the entire structure buckled outward, beginning with the top cinder blocks. Buttressing! I immediately said, as we piled heavy rocks against the cinder blocks. Of course I should have known that all arches exert an outward force that must be accounted for. If the springers sit on the ground, then the earth is your buttress, but if the springers are elevated, something must be done to shore up the bases. We were happy to hear that Dad saw our structure before he died.