Butte was driven to life by rich underground mineral resources. Gold and silver mining grew the city's population from forty men and five women in 1866 to 14,000 by 1885, but copper, critical to the electrification of America, gave Butte a 41 percent share of the worlds copper market and a population of 40,000 by 1910. The city's mineral wealth drew innovative mining technology, capital from figures such as Hearst and Rockefeller, and at least five railroad lines to exploit the resource. Paramount to Butte's development was the need for workers, who came from more than 60 nations and ethnic groups. They worked hard and often gave their lives to mining, making a significant contribution to the labor history of this country. Severe winters and high temperatures underground required miners to build their homes near the mines, in the shadow of tall gallows or head frames, creating a unique landscape of industrial, residential, and commercial buildings. Built on a hillside amid its own industrial lifeblood, Butte played a critical role in the development of the growing nation.