What finally enabled sturdy skyscrapers was sturdy steel, which is a mixture of metals and other elements, such as carbon, which is distinguished by low cost on one hand and strength and flexibility on the other.
Tucked away in the rocky countryside northwest of Cuzco, Peru, Machu Picchu is believed to have been a royal estate or sacred religious site for Inca leaders, whose civilization was virtually wiped out by Spanish invaders in the 16th century.
