For much of its history, New Orleans' skyline displayed only low- and mid-rise structures. The soft soils are susceptible to subsidence, and there was doubt about the feasibility of constructing high rises. Developments in engineering throughout the 20th century eventually made it possible to build sturdy foundations in the foundations that underlie the structures. In the 1960s, the World Trade Center New Orleans and Plaza Tower demonstrated skyscrapers' viability. One Shell Square became the city's tallest building in 1972. The oil boom of the 1970s and early 1980s redefined New Orleans' skyline with the development of the Poydras Street corridor. Most are clustered along Canal Street and Poydras Street in the Central Business District.