In less than 24 hours the Stone Arch Bridge will close for 2 years of restoration. Among the greatest engineering achievements of the 19th century, the story of how it came to be is as big as the structure itself. A SAB #history mega thread! 🧵
1/16 By 1880 Minneapolis had grown from wild, muddy boomtown into the largest lumber and grain milling center on the planet, all from the power of St Anthony Falls. Population swelled 250% in just 8 years, twice the rate of Chicago, St Louis and especially arch nemesis, St Paul.
2/16 19 different railroads snaked through various rickety, overcrowded freight and passenger depots. Several lines went bankrupt just a few years earlier, yet at the same time riverfront mills were producing enough flour each day to fill trains a mile long.
3/16 Over in rival St Paul, business leaders finished
Union Depot in 1881, rationalizing all the capital's transport into one of the busiest and most efficient terminals in the nation. The future of Minneapolis demanded the same, so the city engaged newly-minted magnate James J Hill
4/16 Before a central station could even be contemplated, a new river crossing was needed. The direct route was also the most difficult: any span must survive churning waters at St Anthony Falls, avoid intense milling on each side, and land downtown at busy Hennepin Avenue.
5/16 The impossible project was assigned to Col. Charles Smith, Hill's chief engineer and West Point graduate. Hill envisioned an S-shaped iron span over the top of the Falls, with a northern terminus at Hennepin. Smith worried this plan risked the Falls' collapse.
6/16 Collapse of St Anthony Falls was no idle fear. It almost happened in 1869, when aggressive tunneling to extract yet more power nearly brought it all down. Emergency work saved the last moment and the US Army Corps of Engineers built a massive wood apron across the face for protection in 1876.
7/16 Smith instead designed a span of granite, limestone and marble anchored to the hard riverbed below the Falls. It would be set at a sharp angle and end in a graceful 6-degree curve. With military precision and no expense spared, construction began in January 1882.
8/16 For 22 months, 500-1000 men worked round the clock under electric lights mounted on towers. 5 trains a day brought in stone, carved by hand and placed with block and tackle into 23 arches ranging from 40 to 98 feet wide. 3 men and 1 horse died, a low figure for the day.
9/16 After completion at the end of 1883, the front page of Scientific American hailed the Stone Arch Bridge as the noble engineering achievement of the age. "Hill's folly" was a smash hit and became a widely recognized symbol of Minneapolis.
