The vibrant ten-block district known as the Golden Triangle, at the heart of downtown Pittsburgh , stands at the confluence of the Monongahela, Allegheny and Ohio rivers, once bitterly fought over as the gateway to the West. The French built Fort Duquesne on the site in 1754, only for it to be destroyed four years later by the British, who replaced it with Fort Pitt . Industry began with the development of iron foundries in the early 1800s, and by the time of the Civil War, Pittsburgh was producing half of the iron and one third of the glass in the US. Soon after, the city became the world's leading producer of steel, thanks to the vigorous expansion programs of Andrew Carnegie , who, by 1870, was the richest man in the world. Present-day Pittsburgh is dotted with his cultural bequests, along with those of other wealthy forefathers including the Mellon bankers, the Frick coal merchants and the Heinz food producers. Though saddled with a Victorian reputation for dirt and pollution, the city experienced a transformation after the 1950s. A face-lift involved large-scale demolition of abandoned steel mills, which freed up much of the downtown waterfront, but all-out yuppification has been kept in check by the student population and the small-town feel of the older ethnic neighborhoods to the north and south. Pittsburgh today is one of America's most attractive and most liveable cities; resilience and enthusiasm rather than coal fumes fill the air, and sleek architecture and green parks supplant smokestacks and slums. The popular Andy Warhol Museum , opened in 1994, has bolstered Pittsburgh's image as a destination city, while an enormous new Convention Center will bring in major conferences, which is sure to add to the influx of visitors. Each of Pittsburgh's close-knit neighborhoods - the South Side and Mount Washington , across the Monongahela River from the Golden Triangle , the North Side across the Allegheny River, and Oakland , the university area in the east - attests in its own way to the city's history and its resurgence. Easily accessible from each other, they retain individual identities while remaining part of a proud whole.