Construction of the Golden Gate Bridge took four years and five months during the Great Depression.

On Jan. 5, 1933, after the decade of political, financial and engineering wrangling described in the two previous Portals, construction on the Golden Gate Bridge finally began. It was an epic task, one that lasted four years and five months in the depths of the Great Depression.

The first task was to build the two massive anchorages that would support the bridge’s cables. Enormous pits were blasted and dug out on both the San Francisco and Marin sides, then filled with 270 million pounds of concrete, in which were embedded steel support members 134 feet long, with enormous “eyes” into which the cables would be threaded. It was an undertaking akin in scale to the building of the Great Pyramids.

But the truly Herculean feat was the construction of the bridge’s south tower. No structure of its size had ever been built in such a daunting environment: 1,125 feet offshore, in black water 110 feet deep, scoured by powerful currents. Divers had to first search the strait floor for a suitable site for the pier, working only 20 minutes at a time because of the pressure. Once the site was located, a trestle, or working pier, was run out from Fort Point, and a gigantic concrete oval the size of a football stadium, called a fender, was constructed around the site to protect and enclose it. An unexpected storm washed away the trestle, but it was rebuilt. After the water was pumped out of the fender, engineers descended in a bucket to the ocean floor to make sure the serpentine was strong and thick enough to support the pier. It turned out to be even more solid than they expected. Then heroic amounts of concrete were poured into a giant form in the fender to make the mighty pier that would support the south tower.

The bridge’s elegant, tapering, Art Deco-inspired towers were each 746 feet tall, the height of a 60-story building — the tallest bridge towers in the world at the time. As they rose, it looked like they were building themselves: the prefabricated steel sections were hoisted into position by a giant, movable crane positioned between the tower legs, called a “traveler.” As the tower grew, the traveler climbed up with it, lifting the steel plates higher and higher. There were 44,000 metric tons of steel plates in each tower, the plates fabricated at Bethlehem Steel plants in Pennsylvania. Each tower was held together with 600,000 rivets, which were heated on site in portable coal-burning forges that looked like barbecues. The white-hot rivets would be tossed to the riveters, who would catch them in a cone and grab them with tongs before installing them.

Once the towers were completed, the cables that would hold up the roadway were installed. This crucial task was carried out by John A. Roebling Sons, the cable company founded by the legendary engineer who had built the Brooklyn Bridge. Each individual acid-steel wire was less than a fifth of an inch in diameter, smaller than a pencil, but was so strong a man could not bend one double. These wires were bundled into strands, each strand containing 256 to 462 wires, and tied off with metal bands. The cables were then laid between the anchorages and over the towers, using special spinning machines that traveled back and forth, spooling out the cables. Before the cables were put in place, guide wires were installed exactly in the places where the cables would run. Their placement called for such precision that surveying instruments were used, and the guide wires could be adjusted only at night to avoid heat expansion distorting the measurement.

This combination of incredible strength and extraordinary precision characterized the work on the entire bridge — much of it taking place hundreds of feet in the air. It was dangerous, stressful work, and bridgemen drank hard on the weekends. So many workers showed up on Monday with hangovers that management provided pickle juice as a restorative.

On one occasion, some bridgemen released their tension — and some other substances — on the job. Wooden catwalks had been installed, allowing humans to walk across the Golden Gate for the first time. Portable toilets were installed on these 15-foot-wide catwalks, the waste stored in traps beneath them. Driven partly by anti-Japanese sentiment (Japan had recently seized Manchuria), partly by the irresistible impulse to pull off a nasty practical joke, some workers released a full load from one of the toilet traps as the Japanese freighter Shensu Maru passed beneath, aiming for its smokestack. The contents missed the smokestack but splattered on the ship, causing an angry protest. The perpetrators were never caught, but no such incident ever took place again.

Almost to the end of construction, the safety record on the Golden Gate Bridge was exemplary, even extraordinary. In bridge work, one life lost for every million dollars spent was considered normal, yet in February 1937, with just three months of work left before the $35 million bridge was finished, there had been only one fatality. To his credit, chief engineer Joseph Strauss had insisted on installing a $130,000 safety net, made of manila rope woven into 6-inch squares. The numerous men who fell into this net proudly anointed themselves members of the highly exclusive “Halfway to Hell Club.”

Then, on Feb. 17, 1937, tragedy struck. A 5-ton platform suddenly collapsed, ripping and dragging more than 2,000 feet of safety net down into the sea. Twelve men, captured as tiny specks in a photograph, were sent hurtling 220 feet into the water. All but two were killed. An investigation found that the bolts were faulty. There was much finger-pointing, but no charges were ever filed.

The final job, the installation of the concrete roadway, was completed in April. The catwalks and other temporary structures were removed, and the bridge was revealed in all its glory for the first time.

The Golden Gate Bridge was ceremonially opened on Thursday, May 27, 1937, with a “Pedestrians Day.” Schools and many stores were closed. At 6 a.m., the opening hour, the bridge’s great foghorns emitted their basso blasts, the barriers were removed, and thousands of people poured onto the bridge. The first person to make it across was a San Francisco Junior College sprinter named Donald Bryant. Others raced to be the first skaters, the first stilt-walkers, and the first twins to cross the bridge. There were tuba players, tap-dancers and harmonica players. An estimated 200,000 people walked across the bridge on its opening day.

Previous trivia question: There are 21 Spanish missions in California. The first was Mission San Diego de Alcala. What position on the list is Mission San Francisco de Asis?

This week's trivia question: What did the 19th century term "parlor house" denote?

The Golden Gate Bridge is many things. It is an example of world-class engineering. It is a monument to the skill and courage of the American worker, and of American resilience in the country’s darkest days. But its real significance is larger. Before it was built, some parties, including the Sierra Club, opposed it because they feared it would profane its magnificent site. Their fears were not unfounded: What structure could match the matchless Golden Gate? But they were wrong. The Golden Gate Bridge is that rarest of things, a human creation equal to nature at its most sublime. It is San Francisco’s crowning glory, but it belongs to mankind.

Gary Kamiya is the author of the best-selling book “Cool Gray City of Love: 49 Views of San Francisco.” His most recent book is “Spirits of San Francisco: Voyages Through the Unknown City.” All the material in Portals of the Past is original for The San Francisco Chronicle. To read earlier Portals of the Past, go to sfchronicle.com/portals.