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The Bridge under constructionOn 28 July 1923 JJC Bradfield turned the first sod for the start of construction of the Sydney Harbour Bridge, though the designed was still not complete. It was several years before construction work began in earnest.

At Milsons Point, two vast workshops arose where hundreds of workers toiled round the clock to meet the punishing schedule. Materials were unloaded from steamers by crane, transformed by machines, and fashioned into beams, rivets and joints, then shipped back to the water, and lifted into position by two massive creeper cranes working on either side of the harbour.

Bradfield's planned bridge was massive in every respect. By far the tallest structure in the entire country, the Bridge incorporated 50,000 tons of steel. Indeed, it was the heaviest bridge yet built. The rivets used to hold the structure were bigger than any previously used, and the steel angles were the largest that had ever been rolled.

Adding to the challenge, the depth of the water beneath the Bridge meant that it would not be possible to support the arch while it was being build. Each arm of the arch would have to be held in tension by wire ropes as they crept out across the water.

The Bridge's foundations were dug deep into the sandstone on each side of the harbour, and supported the four giant hinges that would eventually hold the entire weight of the Bridge. Each bearing weighed more than 300 tons. Behind the hinges were U-shaped tunnels through which the anchor cables passed - 128 for each side of the Bridge.

The design required almost inconceivable precision. The arch was constructed from straight sections of steel, brought together at a slight angle. The maximum clearance allowed was 4/1000 of an inch (0.1mm) between angles. When the two halves of the arch eventually met, there was a combined error of only half an inch (13mm).