We may live in an era of information abundance, but it's often simple symbols that focus our attention. The ninth anniversary of 9/11 is, finally, bringing new symbols at Ground Zero.

Until recently, the dominant symbol has been the site itself—an empty plot in the middle of the world's most bustling financial district. In the past few months, the Port Authority of New York and New Jersey finally got above ground rebuilding on the site.

The Twin Towers were attacked as symbols, representing to radical Islamists the essence of Western capitalism and culture. Some 2,000 construction workers are creating new symbols on the eight-acre site. Freedom Tower (officially called 1 World Trade Center) is one-third complete toward its 1,776 feet. Future tenants include publisher Condé Nast and a Chinese business and cultural center. The memorial where the Twin Towers stood will be the country's largest man-made waterfalls. The corner of Church and Vesey Streets, on the northeast corner of the site, is the busiest pedestrian crossing in the U.S.

The Ground Zero site now, with the partially complete 1 World Trade Center (Freedom Tower) on the left. Associated Press

There are less encouraging symbols of 9/11, including the provocation of a planned mosque two blocks away. But rebuilding the site is a sign that the leading commercial city is no longer paralyzed.

There was similar symbolism nearly a century ago when Wall Street was first targeted by a terrorist attack against modern capitalism. On Sept. 16, 1920, a bomb placed on a horse-drawn cart parked at the corner of Wall and Broad Streets exploded, killing 38 people and injuring hundreds.

Yale historian Beverly Gage last year described in "The Day Wall Street Exploded" how this terrorist attack, with anarchists as the likely perpetrators, came when "million of people around the globe believed that capitalism was on the verge of collapse."

Wall Street reacted by getting back to business as quickly as possible. A Wall Street Journal editorial the day after the blast said it "killed an uncertain number of absolutely innocent and uninterested people," sending "a sufficient number of injured to the neighboring hospitals to make it a total record of casualties about equaling a raid in France in No Man's Land during the late war. And that is all it did." The editorial added, "The relations between capital and labor will not be changed, not even for the worse as regards labor; for no one but a fool has ever doubted Wall Street's courage."

But as with today's Islamists, the anarchist threat was real. Anarchists had bombed and killed many at Chicago's Haymarket Square and the Los Angeles Times building, and had tried to mail bombs to 30 people, including J.P. Morgan, John D. Rockefeller, and the mayor and police commissioner of New York City. Anarchists had assassinated President William McKinley, a Russian czar, a French president, a Spanish prime minister and the king of Italy.

The memorial to the earlier attack on Wall Street is unusual: damage left unrepaired. The bomb, made up of dynamite and hundreds of cast-iron slugs, went off across the street from the headquarters of J.P. Morgan, then the world's leading bank. It left deep pockmarks in its marble outer walls, which the partners left as an act of defiance.

In his 1969 classic about Wall Street, "Once in Golconda," John Brooks described this memorial. "The monument consisted of scars that were allowed to remain untouched on the north facade of 23 Wall Street . . . ragged and eye-catching, an inch deep in places and suggesting moon craters as seen through a telescope," he wrote. "No plaque explained them, or was necessary; the passer-by who stopped to stare at them soon came to draw the knowing and superior smile that a native bestows on a tourist anywhere." A J.P. Morgan partner explained the pockmarks: "It's right and proper that they should stay there."

Yet by the fifth anniversary of the bombing, a report in the Journal found that even people who worked in the financial district didn't know what caused the pockmarks. "How quickly time effaces the memory of startling events," this newspaper concluded. One reason is that anarchist attacks had been nearly eliminated soon after the bombing.

Symbols of remembrance and rebuilding are important tools of communication. Psychologist Robert Jay Lifton has written that people "live and die, succeed and fail, delight and suffer, work and play, with, by and through their symbols." The Athenians refused for years to rebuild the Parthenon after the temple was destroyed in a war with the Persians in 480 B.C., because they had pledged to leave its ruins as "memorials to the impiety of the barbarians."

For its part, the old J.P. Morgan headquarters is a symbol of a new kind. In 2003, it was converted into a designer condominium called "Downtown by Philippe Starck," part of a post-9/11 residential resurgence in the financial district. The new owners have left the 1920 pockmarks in place.