Chicago and New York offered a handful of very different preconditions that influenced the way skyscrapers were designed and built in the two cities. Chicago’s murky soil forced engineers to carefully parse their structures into point supports and broad, snowshoe-like pads, which suggested structures above could be thought of as more skeletal frames than continuous walls. The city’s large, regular lot sizes also allowed a regularity in structural grids, and its laissez-faire politics permitted thinner walls than other, eastern cities—at least through 1893, after which unions and builders began a pitched battle over the city’s building code. The first session of the Construction History series focuses on Foundations to consider a “ground up” understanding about how buildings were constructed in each city, given the local conditions. Although Manhattan had abundant bedrock, even some of the tallest 19th-century skyscrapers did not rely on it. Small lots and slender towers were common conditions in the dense financial district, whereas Chicago’s big blocks and soft soil posed different problems.