High wire artist Philippe Petit electrified New York City -- and the world -- with his early morning walk between the twin towers on August 7, 1974. Here he discusses his preparation for the walk and the high wire journey itself.

Historian Niall Ferguson talks about the American Experience of globalization, globalization's political dimension, and 9/11 as a turning point.

Photographer Camilo Jose Vergara discusses the visual impact of the World Trade Center from different perspectives.

Engineer for the World Trade Center, Leslie Robertson discusses architectural aspects of the buildings, including the sculptural quality, close columns and narrow windows, the skin structure, and the comparison to the Empire State Building.

Former New York governor Mario Cuomo talks about lessons learned from 9/11 and evolving toward a new civility.

Architecture critic Ada Louise Huxtable discusses the options for building at Ground Zero and speaking to the spirit of the location.

President of the World Trade Center Association, Guy Tozzoli, discusses the planning, construction and operation of the World Trade Center.

Historian Mike Wallace discusses the US and global interests, Lower West Side business, and the opposition to building the World Trade Center.

Architectural historian Carol Willis discusses the opposition to the World Trade Center, the public's opinion of skyscrapers, and rebuilding at Ground Zero. Willis was interviewed during the making of Ric Burns' New York: The Center of the World.

Writer Pete Hamill talks about New York before the World Trade Center, the New York economy, what was destroyed to build the towers, and getting used to the World Trade Center.

The south tower of the Golden Gate Bridge was built over a thousand feet into open ocean. To build the tower, workers would have to erect a pier more than 1100 feet out in the middle of the Gate -- the first bridge support ever constructed in the open ocean. Divers guided beams, panels, blasting tubes and 40-ton steel forms into position and secured them, striving to avoid being swept away.

Construction on the bridge began in January 1933. Workers excavated 3 1/4 million cubic feet of dirt to make way for the bridge's anchorages, one on each side of the Gate.

Working twelve to fourteen hours a day, Charles Ellis personally computed dozens of factors, and completed the bridge's overall design in four months. In November 1930, Strauss directed Ellis to begin the thousands of detail calculations involving suspension ropes, decks, floor beams, highway track, cables, towers, and more.

The first 745-foot tower began to rise in Nov. 1933. Prefabricated sections were fit into place and then joined together by four-man rivet gangs. The heater was the boss; he brought rivets to the right temperature on a small forge, then tossed them to catchers with metal cans.

Cable spinning began in October 1935. To create the cables, Roebling developed a method called parallel wire construction. The innovative technique enabled a cable of any length and thickness to be formed by binding together thin wires. Hundreds of wires, each roughly the diameter of a pencil, were bound together into strands. Hydraulic jacks then bundled and compressed 61 strands to make a cable.

Chief Engineer Joseph Strauss hired a local architect, Irving Morrow, to design an architectural treatment for the bridge. Morrow would later be recognized for his aesthetic contributions: the Golden Gate Bridge's distinctive Art Deco lines, burnt red-orange hue, and the structure's dramatic lighting.

Emma Goldman's anarchist politics and outspoken activism against capitalism, wars, and the oppression of women captivated and polarized the American public for nearly thirty years.

American Anarchists in the 1880s were a small but powerful movement who advocated radical ideals of universal human equality, education for all, and an end to state government.

In June 1892, workers at the Andrew Carnegie-owned steel plant in Homestead, Pennsylvania went on strike. When plant manager Henry Clay Frick hired 300 armed guards to attack strikers, the resulting battle ended in deaths on both sides.

The Panic of 1893, a severe economic depression, created public awareness of the growing gap between the rich and the poor. Emma Goldman organized demonstrations and encouraged unemployed Americans to demand jobs and food from the wealthy.