Malcolm X appears in Boston public television producer Henry Morgenthau III's "The Negro and the American Promise," alongside Martin Luther King and James Baldwin. After watching the segment a viewer wrote that he was shocked "that such a blatant display of racial prejudice could be aired."

The foundations themselves presented the first challenge. They would have to descend through 70 ft. of water-logged landfill before reaching bedrock. The greatest challenge by far, however, lay in the engineering of the towers themselves. The solution, developed by the structural engineers John Skilling & Leslie Robertson in the mid-1960s, was to re-conceive the basic structure of tall buildings.

The structures needed not only to support the sheer weight of the 1,360-ft-tall buildings, but to overcome the even greater loads caused by the high winds of New York Harbor pushing against the wide, flat sides of the buildings, especially along their uppermost floors. The solution: a super-strong lattice of exterior steel columns, creating a remarkably stiff "tube" that could resist high winds.

As the World Trade Center towers began to rise, another innovation made its appearance. Unlike earlier skyscrapers, assembled one column or beam at a time, the twin towers were erected in huge prefabricated components. Exterior wall sections three stories tall and floor decks 60 feet long could be lifted into place at once. The daring new technique dramatically speeded the construction process.

The design and construction of the twin towers of the World Trade Center marked a dramatic break with nearly a century of skyscraper tradition. The unprecedented height and size of the towers posed a new kind of structural challenge. They needed not only to support the sheer weight of the 1,360-ft-tall buildings, but to overcome the even greater loads caused by the high winds of New York Harbor.

Before they could sign off on the design for the World Trade Center, engineer Leslie Robertson and his team had to consider all possible events that might take place in a high rise building. One of these possibilities was that of an airplane impact—there had been two incidences of aircraft impact on New York City skyscrapers at that time.

Engineer Theodore Judah solved the great riddle of the Pacific Railroad when he reached Donner Pass. Judah immediately recognized the location as ideal for constructing a line through the Sierra Nevada. Judah's plans called for bridging rivers and ravines, carving 20-foot wide shelves out of sheer mountain faces and driving 18 tunnels -- one more than a 1000 feet long -- through solid granite.

While tunnels were being dug through the limestone and quartzite mountains of Utah, Union Pacific workers laid track in western Wyoming. In the Wyoming desert, temperatures would soar above 100 degrees by day and fall below freezing at night.

To get the railroad line across Cape Horn -- 1,300 feet above the valley floor -- workers had build a ledge for the track to run. The dangerous work involved chiseling and carving away the cliff face by hand in a narrow space just wide enough for a worker to walk through.

In the fall of 1866, as the Central Pacific completed its track to Cisco, 92 miles east of Sacramento, Chinese work gangs were hurried to Donner Summit, where seven separate tunnels had to be dug. The most difficult was number six, the Summit Tunnel, 1,659 feet long and through some of the hardest rock in North America. Forty-four snow storms hit the summit that season.

The Central Pacific prided itself on its workmanship.

The Central Pacific's best hope was a dangerous gamble: liquid nitroglycerin. Nitro was the most powerful explosive ever made, and the least stable. Transportation of liquid nitro was made illegal in California in 1867, but a British chemist came and mixed the compound on site. Liquid nitro helped the workers by blasting more rock in much less time.

At a church on the South side of Chicago, thousands paid tribute to Emmett Till by attending his funeral. It seemed as if all of Chicago was there, and the reaction of blacks was visceral.

Emmett Till's great-uncle and cousin remember the night he was taken; it was a terrifying experience.

No one ever did time for the killing of Emmett Till, a fourteen year old black boy from Chicago, but his murder, and the trial and acquittal of his killers, sent a powerful message, and his sad story spurred the Civil Rights movement.

The trial of J.W. Milam and Roy Bryant for the murder of Emmett Till ended just 5 days after it began, with their acquittal. But reports of the acquittal set off an international firestorm.

50,000 people in Chicago saw Emmett Till's corpse with their own eyes. Photos of Till were published in newspapers and magazines, and even white Americans were stunned by the brutality of the murder.

Hundreds of thousands of black people fled Mississippi for Chicago in the years between the world wars. Neighborhoods and schools were segregated, but the city offered a kind of freedom black Mississippians could only dream about.

An excerpt from a 1960 film by the Mississippi State Sovereignty Commission, an anti-civil rights agency.

WARNING: GRAPHIC CONTENT: Lynching was a danger African-American men faced throughout the South. if a white person harmed a black person there was absolutely no recourse.