The city was founded on the site of the Native American town of Shannopin, a late-17th-century fur-trading post at the junction of many canoe routes and trails. Fort Duquesne, built by the French in the middle of the 18th cent., later fell to the English and was renamed Fort Pitt. The village surrounding the fort was settled in 1760, and it prospered with the opening of the Northwest Territory. At the height of industrial development in the late 19th cent., Pittsburgh was a hotbed of labor unrest and union movements. The "Steel City" was once also called the "Smoky City" because of severe pollution; the problem, however, gradually abated by the late 1970s as industrial production fell. Sprawled over a hilly area, Pittsburgh has become an attractive city, but the loss of steel industry jobs has also led to a population decline. The business district was refurbished and marked by a construction boom that began in the 1980s.