Why Triangles are important in building and construction?

Why Triangles are important in building and construction?

Triangles are important because you can use different materials to tension or compressed. When you build a house there are triangles in the roof which help the wind go over the roof easily. Also when you put pressure on the top of the triangle the sides of the triangles compress and the bottom of it tensions. 
When you use tension you tension the material eg rope, fabric etc. would tension and would try to pull apart so when you cut it the rope or fabric would pull back to where it was bolted in. 
But when you want to use compression is when you put support on a platform which is made out of materials eg wood, metal, etc. would compress so when it was cut it would go past each other. 

 http://abnormalimage.com/images/tension.view.jpg  an image of tension.

http://upcouture.com/img/cms/Compression_Spring_Posture.jpg an image of compression.