'Once-Lowly' Piece of Infrastructure Honored as a Hero of 9-11

David W. Dunlap recounts how the slurry wall built around the World Trade Center's foundations prevented the devastation to Lower Manhattan from becoming much worse, and "became a symbol of resilience in the months and years after the attack."

1 minute read

September 11, 2013, 10:00 AM PDT

By Jonathan Nettler @nettsj


After it was built over nine months beginning in 1967 "using jury-rigged tools, on a site that brimmed with uncharted obstacles and unhappy surprises", engineer Arturo Lamberto Ressi di Cervia never thought he'd see the retaining wall he helped construct again in his life. But the events of Sept. 11, 2001 changed that. 

"Because the slurry wall held, the 70-foot-deep foundation did not fill with groundwater [when the towers fell]. And because of that, the PATH tubes were not submerged. And because of that, the subway tunnels below the PATH tubes were not inundated," explains Dunlap. "How much worse could Sept. 11 have been? Imagine if Hurricane Sandy had followed the terrorist attack by a few hours."

"Thirty-five years later, in 2002, the architect Daniel Libeskind drew the world’s attention to the symbolic significance of the wall, when he proposed its preservation and exposure as part of the redevelopment of the trade center."

Wednesday, September 11, 2013 in The New York Times

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Cover CM Credits, Earn Certificates, Push Your Career Forward

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

June 25, 2025 - Diana Ionescu

Map of Western U.S. indicating public lands that would be for sale under a Senate plan in yellow and green.

Map: Where Senate Republicans Want to Sell Your Public Lands

For public land advocates, the Senate Republicans’ proposal to sell millions of acres of public land in the West is “the biggest fight of their careers.”

June 19, 2025 - Outdoor Life

Person wearing mask walking through temporary outdoor dining setup lined with bistro lights at dusk in New York City.

Restaurant Patios Were a Pandemic Win — Why Were They so Hard to Keep?

Social distancing requirements and changes in travel patterns prompted cities to pilot new uses for street and sidewalk space. Then it got complicated.

June 19, 2025 - Diana Ionescu

Close-up of full beer glass with purple train-themed design sitting on bar between two frosty tall cans.

Platform Pilsner: Vancouver Transit Agency Releases... a Beer?

TransLink will receive a portion of every sale of the four-pack.

June 30 - Cities Today

Vintage red Toronto streetcar passing in front of Rogers Arena in Toronto, Canada.

Toronto Weighs Cheaper Transit, Parking Hikes for Major Events

Special event rates would take effect during large festivals, sports games and concerts to ‘discourage driving, manage congestion and free up space for transit.”

June 30 - blogTO

Map of Berlin with ring roads in green and red.

Berlin to Consider Car-Free Zone Larger Than Manhattan

The area bound by the 22-mile Ringbahn would still allow 12 uses of a private automobile per year per person, and several other exemptions.

June 30 - Streetsblog USA

Urban Design for Planners 1: Software Tools

This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.

Planning for Universal Design

Learn the tools for implementing Universal Design in planning regulations.