What Was Under the Twin Towers? The Wall That Held Back the Hudson

What’s under the Twin Towers? A massive slurry wall called the “bathtub” kept the Hudson River and groundwater out while engineers dug deep into Lower Manhattan. This hidden structure made the World Trade Center foundations, six basement levels, and PATH terminal possible. See how bentonite slurry, reinforced concrete, tieback anchors, and careful excavation sequence turned old landfill into a dry construction site—and how the wall later helped protect Ground Zero after 9/11. It’s the story behind the Twin Towers foundation most people never saw.