Roof by mr. rollers. Flickr. (CC BY-NC-ND 2.0)

Once, two friends were disputing about the structure of buildings, and why the roof does not fall down. They agreed to do some research, so each set out in search of a good example to study.

Walking in the woods, the first man came across a large and splendid building, and stepped inside. He saw that the structure was made of stones piled on top of one another, with mortar in between. He stayed for a while and made a close study of the stones and the mortar.

Meanwhile the other man was walking in the fields when he spied a tall building, and made his way towards it. Stepping inside, he was immediately struck by the tall wide walls with buttresses, and the many pillars and arches which supported the roof. He stayed and made a thorough study of…