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'Going Home': The world looks back

'Maybe that's why I was there that day'

A piper follows a flag bearer in a march from the Bronx toward Ground Zero in Manhattan.

(CNN) -- In the deep of the night they've started marching -- to honor those killed in broad daylight. Well before dawn, a day of nationwide commemoration unique in American and world history has begun.

Bagpipe and drum processionals started moving as early as midnight Wednesday from each of New York's five boroughs, their ancient keens echoing against darkened streets and buildings as they made their way to lower Manhattan.

By 8 a.m. ET, they are scheduled to reach Ground Zero, where officials now say 2,801 people lost their lives in the cataclysmic terrorist attacks of September 11, 2001. (Full story)

Some 300 musicians will form a circle of honor on the floor of the World Trade Center site. They will pipe the plaintive "Going Home" Largo theme of Dvorak's symphony "From the New World" and then fall silent at 8:46 a.m. ET, the time at which American Airlines Flight 11 slammed into the Trade Center's North Tower a year ago.

EXTRA INFORMATION Follow an interactive timed schedule of the September 11 commemorative events  planned for Ground Zero, the Pentagon and Shanksville, Pennsylvania.

By day's end, memorial services will have been held at Ground Zero; at the Pentagon; in a field at Shanksville, Pennsylvania; at St. Paul's Cathedral in London; at the new dome that gleams atop the German Bundestag in Berlin; at the American Embassy in Paris; in towns and cities across the United States; and in an international series of performances of Mozart's Requiem in concert halls from Tokyo to Belgrade, from Lisbon to Honolulu.

But despite the soul-bracing reach of these many events, a sense of peace may be hard for some to find.

It is in a context not only of profound sadness but also of raised national alert and nagging worry -- about the new scope of modern terrorism -- that people in many parts of the world Wednesday will pause to contemplate the vast vulnerability of civilization exposed on September 11.

Highlights of the day

CNN NewsPass Video    •  A musical tribute to 9/11   •  Smithsonian unveils 9/11 exhibit   •  U.S. threat status 'High'   •  A musical tribute to 9/11   •  Homeland Security on high   •  Bin Laden on 9/11   •  Al-Jazeera tape shows 9/11 hijackers   •  Life the day before 9/11   •  Man survives 9/11 by chance   •  Has air security improved since 9/11  MORE STORIES   •  Detainees reveal bin Laden's reaction   •  Al-Jazeera: Hijackers boast on tape   •  U.S. issues 'worldwide caution'   •  NYC's top cop: 'I think we're ready'   •  Entertainment, a year later   •  Museums mark September 11 anniversary  EXTRA INFORMATION   •  Flash timeline: September 11   •  Faces of September 11   •  Fighting Terror  RESOURCES   •  In-Depth: America Remembers   •  Schedule: CNN TV, live streaming video   •  Scheduled commemorative events   •  In-Depth: War Against Terror   •  In-Depth: How prepared is your city?   •  Time.com: September 11: A Nation Remembers

Activities will be punctuated by periods of silence and the coordinated pealing of bells to mark significant moments during the attacks -- the times of the four hijacked jetliners' impacts, the collapses of the North and South Towers of the Trade Center.

Among international observances are a service in London's Grosvenor Square at the U.S. Embassy to be attended by British Prime Minister Tony Blair; an ecumenical service at the Berlin Dome with German Chancellor Gerhard Schroeder; and a ceremony at the U.S. Embassy in Paris, with French President Jacques Chirac in attendance. In addition, a program called the Rolling Requiem will open the first of a global string of performances of Mozart's Requiem with performances in New Zealand starting at 8:46 a.m. ET. Europe, too, is on high alert for the September 11 anniversary. (Full story)

Key observances in the United States are flanked by hundreds of similar ceremonies, concerts and vigils in parks, churches and other venues around the country. Some 150 art museums are participating in a coordinated project of September 11-related artwork. (Full story)

Conflicting emotions

A marble marker at the site of United Airlines Flight 93 in Pennsylvania commemorates the phrase "Let's roll," said by passenger Todd Beamer shortly before the plane crashed.

However carefully planned and lovingly executed are these ceremonies, they take place amid starkly mixed feelings.

For many people, the main response simply is fear.

In the run-up to the anniversary of the attacks, the U.S. State Department issued a worldwide caution urging American citizens to be vigilant because "the U.S. government has continued to receive credible indications that extremist groups and individuals are planning additional terrorist actions against U.S. interests," according to the statement. "Such actions may be imminent and include suicide operations." (Full story)

And Tuesday, the Office of Homeland Security raised the official threat level from a yellow, or "elevated" level of vigilance, to an orange, or "high" rating. The threats, said Bush, "remind us of the pattern of threats we heard prior to September 11," 2001. (Full story)

Nevertheless, comfort is being held out to the American community as it comes together, by law enforcement workers and administration officials made newly watchful by the events of September 11.

Even as news of the heightened alert status was announced, Bush counseled Americans to "go about their lives. They just need to know that their government, at the federal and state and local level, will be on an extra level of alert to protect us." (Homeland Security terror warning system)

And in New York, Police Commissioner Raymond Kelly said, "We'll have, I believe, appropriate resources in place, and in the right places, to address any event that may happen." (Full story)

Workers put finishing touches on the rebuilt portion of the Pentagon in preparation for Wednesday's commemoration services.

Granted, no amount of reassurance can ease all nerves on a day so reflective of such violence, especially with news of an elevated state of alert.

But messages of determined hope, however darkened by sadness, are heard in comments like those of the Pentagon's Sgt. Maj. Tony Rose, who told CNN about pulling nine people out of harm's way:

"For a while, there was some guilt associated with why didn't I die that day. But later as we took a look at the map of where people had died, I was assured to see that there was no one [lost] in the sector where I was -- we'd gotten them out.

"Maybe that's why I was there that day."