 Prior to the late-nineteenth century, the weight of a multi-story building had to be supported principally by the strength of its walls.The taller the building, the more strain this placed on the lower sections of the building; since there were clear engineering limits to the weight such "load-bearing" walls could sustain, tall designs meant massively thick walls on the ground floors, and definite limits on the building's height.The development of cheap, versatile steel in the second half of the nineteenth century changed those rules.