When it was constructed in 1895, Milwaukee’s City Hall was the third-tallest building in the country, and it remains one of the oldest continuously used city halls.
But its story begins hundreds of millions of years ago when its building materials began to form.
Raymond Wiggers, architectural geologist and author of Milwaukee in Stone and Clay, says the oldest of City Hall's building materials is Holston Limestone, or "Tennessee Marble," which began to form about 450 million years ago.
"It comes from what is now eastern Tennessee [...] but comes from a time when that area was a continental shelf off the edge of what is now North America," Wiggers says. "Eventually what happened is another land mass collided with that side of the continent, and scrunched this material up."
Holston Limestone can be found in the interior, in the side panels of the main rotunda chamber. The stone works with other material to create a kind of M.C. Escher-style optical illusion. But it is unclear if this effect was intentional or a circumstance of building a round interior on a triangular plot.
"I wasn't able to determine whether or not it was a conscious effect Henry Cook was driving for," Wiggers says. "But I think his brilliant design of cast iron railings on different levels [...] if you look up for too long you can really get vertigo."
Down at the bottom of City Hall lies another geological and architectural wonder: Berea Sandstone. This stone is found at the bottom of the building today but began its life about 350 million years ago in what is today northern Ohio. But this was a time when Ohio and Wisconsin were part of Pangea and located near the equator.
"At that point, there was an inland sea that covered a good portion of the Midwest," Wiggers says. "Near where Cleveland is now, there was a large river delta [...] forming sand deposits which are now considered very high-quality building stone."
To anchor the Berea Sandstone and the rest of the building into what was historically marshland, Wiggers says large tree trunks, or piles, were driven deep into the ground to anchor the structure. That system worked for decades, but eventually, the piles began to rot due to changing underground water levels.
Wiggers says eventually these wooden piles needed to be amended as they decomposed. Beginning in the mid-20th century, steel tubes called "micropiles" were driven into the ground around the original wooden piles.
"So as the original piles rot away, these metal supports will actually take up the load completely," Wiggers says.
Wiggers mentions other materials used in the building, from St. Louis brick to Winkle terra cotta, both dating back about 300 million years. But what is missing from City Hall's architectural geology is locally sourced materials, such as Cream City brick.
While Wiggers notes that he doesn't know exactly how the architects chose to source materials from elsewhere, he believes it came down to a combination of economics and fashion.
"The architect and designers probably had a particular color scheme they wanted, which was not provided by local materials, so they went with other stone," Wiggers says.
Wiggers added that while Cream City brick is used in residences and public buildings around the world, it's not a popular choice for city government buildings in Wisconsin or elsewhere.
"There's a very famous old church in Chicago that survived the 1871 Chicago Fire, called Old St. Pat's, that is made of Cream City brick," Wiggers says. "But city halls? No, I don't think so."
