The remains of the beehive coke ovens visible on both sides of the Youghiogheny River are among the first in what became known as the Connellsville Coke Region, where more than 35,000 ovens eventually operated. Coke, a hard, porous residue with a high heating value, was made by burning coal in sealed ovens. When it was ready, the coke was drawn from the ovens, loaded into rail cars, and shipped to Pittsburgh for use in making steel. Until the end of World War I, the Connellsville Coke Region was so unrivalled in coke production that it was at one time known as the Coke Center of the World.