During construction of the Golden Gate Bridge, engineers used aerial cable spinning, completing the main cables in six months and nine days before the bridge opened in 1937

Visualize the Golden Gate Strait in 1935, with a mile-wide gap of churning, cold waters and currents so powerful that they could capsize a ship. Then, imagine several hundred men standing on nothing but two steel wires suspended in the air at five hundred feet above the ground while they weave pencil-thin strands back and forth across the span manually, one by one, until they had created two cables that were sturdy enough to support the whole structure.

That’s the real history behind the construction of the Golden Gate Bridge’s main cables. According to the Golden Gate Bridge Highway and Transportation District’s official page, cable spinning began in October 1935 and wrapped up on May 20, 1936; a total of six months and nine days to spin all 27,572 separate wires per cable. The bridge itself opened nearly a year later, on May 27, 1937, once the roadway deck, paint, and remaining work were finished. This is one of those facts that just sounds insignificant at first, until you begin to realize what it really implies: the team of engineers in the depths of the Great Depression managed to build the largest bridge cables the world had ever seen.

The impossible problem hiding above the water


One thing people hardly mention about suspension bridges is that their cables don't come from someplace else and then get set up on a bridge. There is no way they can be moved from place to place since they are too heavy and too long. Each of the finished cables is about 7,650 feet long, a little over three feet in diameter, and weighs roughly 12,000 tons, according to the Golden Gate Bridge Highway and Transportation District's own account of the build. So there was no other choice but to install the cable right where it was supposed to stay, mid-air over the water.

This technique is known as aerial spinning, and it is remarkably simple in conception. They started by threading a single wire from the anchorage on one shore, up and over the top of both towers, through to the anchorage at the other end, looping it, and sending it straight back again. That basic back-and-forth loop wasn't done just once at a time, though, multiple spinning wheels ran simultaneously along a system of carriages, eventually moving six wires across the strait at once and laying out as much as 1,000 miles of wire in a single eight-hour shift, according to PBS's American Experience account of the build. Run enough times by enough wheels working in parallel, that process built up to the 27,572 individual wires that made up each finished cable, before they were compressed into one thick cable with hydraulic jacks. As stated in the Library of Congress’ Historic American Engineering Record, which recorded the history of building this bridge, the parallel-wire technique enabled engineers to build a cable of any length desired.

The wild timeline that still makes engineers raise their eyebrows

The timeline is truly remarkable in its comparison to the schedule. Roebling's Sons had been allotted roughly 14 months to spin the cables, a figure reported by both PBS's American Experience and Mental Floss's history of the build, and finished in six months and nine days, around eight months ahead of schedule. Multiple strands were spooled out at once, each a different color so as not to get mixed up, with teams switching halfway across the span.

However, despite all the precautions taken to make sure that everything would go well, construction of the Golden Gate Bridge as a whole took many of the workers’ lives even before it was completed. It was a terrible toll that, for its time, was shockingly still viewed as relatively low, only due to the fact that Strauss’s crew provided the workers with safety helmets and safety nets, which most 1930s worksites did not have. The speed record is a fact. So is the cost of the human lives that allowed it.

Why a 90-year-old cable trick still matters

This bridge was declared a National Historic Civil Engineering Landmark in 1984 by the American Society of Civil Engineers, and it continues to hold up as an example of what can be achieved when ambition, dedication, and determination come together to turn a 14-month engineering schedule into a job finished in just over six. In an age where American infrastructure projects may often exceed their deadlines and budgets, there is a certain uneasiness in looking back at a 1930s team who did the exact opposite, without a computer, drone, or Gantt chart in sight.