Which architectural and engineering advances enabled the skyscraper and transformed urban skylines in the late 19th and early 20th centuries?

• A. Wooden frame construction and steam elevators.
• B. Stone arches and brick facades.
• C. Reinforced concrete and radial floor plans.
• D. Steel-frame construction, elevators, and other advances.

Answer: (D)

The ability to rise into the sky hinges on a structural system that can carry the building’s weight independently of the exterior walls, paired with reliable means to move people vertically. Steel-frame construction provides a skeleton that bears the load, so walls can be thinner and non-load-bearing, freeing interior space and enabling many stories. Combined with elevators, which make moving dozens of floors practical and efficient, tall buildings become feasible and useful for dense city cores. These advances—steel frames, safe and efficient elevators, and related innovations like improved fireproofing and mechanical systems—together transformed urban skylines in the late 19th and early 20th centuries. Other options rely on older construction methods that either limit height or don’t define the skyscraper era in the same way.