The important point of Monier's idea was that it combined steel and concrete in such a way that the best qualities of each material were brought into play. Concrete is easily procured and shaped. It has considerable compressive or crushing strength, but is somewhat deficient in shearing strength, and distinctly weak in tensile or pulling strength. Steel, on the other hand, is easily procurable in simple forms such as long bars, and is extremely strong. But it is difficult and expensive to work up into customized forms. Concrete had been avoided for making beams, slabs and thin walls because its lack of tensile strength doomed it to fail in such circumstances. But if a concrete slab is reinforced with a network of small steel rods on its undersurface where the tensile stresses occur, its strength will be enormously increased.