By 1900, Coplay’s cement plant was a smoky, dusty, noisy industrial complex where trains brought coal from the nearby northern anthracite fields and local cement rock, a form of limestone, to towering kilns that produced vast quantities of cement for a growing nation. The industry’s key innovator was David Saylor, who in 1871 received the first American patent for high-quality Portland cement, and by 1894 Saylor’s Coplay Cement Company had built these kilns. During the plant’s heyday, workers loaded bricks made from ground cement rock into the tops of the kilns, laborers shoveled in coal on the second level, and temperatures above 2000 degrees Fahrenheit turned the rock into clinker that was then ground into cement. By 1900, the Lehigh Valley produced three-quarters of all Portland cement used in the United States. Despite long hours, hard labor, and clinging cement dust, Eastern European immigrants and local residents flocked to the mills, while ethnic social clubs and churches helped groups form their own communities. The kilns soon became obsolete after the Atlas Cement Company in nearby Northampton built America’s first rotary kiln, which saved money and labor, and in 1904 the fires in these kilns went out forever.