Minneapolis was a tiny burg when the Stone Arch Bridge brought grandeur and elegance to the city's industrial riverfront. Even amid a modern-day metropolis, the bridge remains one of the area's most eye-catching landmarks.

Older than most historic buildings still standing in the Twin Cities, the 136-year-old bridge has long been Minneapolis' de facto welcome mat. Before it was a hot spot for sightseeing and wedding photos, railroad passengers peered from their windows down at St. Anthony Falls as their trains followed the bridge's gentle curve into downtown.

That bridge's diagonal orientation was on the mind of a Star Tribune reader who wanted to know why it cuts across the Mississippi River at such a peculiar angle. The question was submitted to Curious Minnesota, our community-driven reporting project fueled by questions from inquisitive readers.

The answer has more to do with logistics than aesthetics.

Minneapolis had a railroad problem in the 1880s. Apart from a rickety suspension bridge, there was no efficient method of bringing goods and passengers into downtown Minneapolis from key rail tracks on the east side of the river. So city leaders called upon James J. Hill, who owned the main rail connection between Minneapolis and St. Paul, to develop a solution.

Their goal was to eventually bring trains into a Union Depot that would be erected near the intersection of Nicollet and Hennepin avenues. Hill initially considered taking a more direct route with a new bridge across Nicollet Island, according to an authoritative 1987 history of the bridge published in Hennepin History Magazine.

But his engineer, Col. Charles C. Smith, was wary of disrupting the sandstone river­bed above the falls — which was already eroding — and perhaps fundamentally altering the water power fueling the city's industry. A catastrophic collapse caused by the construction of a tunnel a dozen years earlier was still fresh in people's minds, according to the magazine. They were also worried about the bridge's pillars creating ice and logjams.

Instead they decided to play it safe and build the bridge below the falls, just upstream from where Hill's tracks ended (near today's Dinkytown). It would cross at a diagonal — with a 6-degree curve at one end — so trains could easily travel into the riverside rail yards on their way to and from the proposed depot.

Speed was an important factor. Most railroad bridges of the day were fragile timber structures that trains had to traverse slowly, said Ray Lowry, a Worthington history teacher who wrote the 1987 article.

"Hill didn't want that," Lowry said. "He wanted something that was permanent, something that those trains could steam over at full speed."

The depot opened in 1885. It eventually became so popular that a new depot was required, prompting the construction of the Great Northern Depot in 1914, according to Lowry's history. That building was demolished in 1978.