the bathtub, built in 1967–1968, encompasses a large, roughly rectangular excavation down to bedrock surrounded by reinforced concrete walls, intended to serve as dams to prevent water intrusion from the nearby hudson river (north river). it enclosed nearly the entire original world trade center. the world trade center site was located on man-made water-clogged landfill that had accumulated over centuries, providing an extension of land out onto the hudson river from the original manhattan shoreline, with bedrock located below. manually removing water from this area would have severely altered the water levels surrounding the world trade center site and thus jeopardize the foundations of nearby buildings, causing them to sink. this is why the bathtub method was used.