In the days following the 9/11 attacks that brought down the World Trade Center's Twin Towers and badly damaged the Pentagon, the skies across the country were empty of civilian aircraft.

Three days after those attacks, on Sept. 15, 2001, six hikers packed an American flag measuring 96 square feet, 10 yards of PVC tubing, 100 feet of rope and rolls of duct tape up the White House Trail on Mount Liberty.

It was a cool day, with the Mount Washington Observatory posting a high of 34 degrees for the day, but by 6 a.m., the partial fog on the 6,288-foot peak was giving way to partly sunny conditions, with visibility reported at 40 miles.

Mount Liberty, at 4,459 feet, is nearly 2,000 feet lower than Washington, but it's likely that the weather on top of this Franconia Ridge summit was similar to Washington's when the six hikers hoisted the flag on top of its rocky outcrop.

The hiking community has continued to honor those who died in the attacks by flying the American flag at the summits of all 48 mountains 4,000 feet and higher in New Hampshire. This year is especially noteworthy, as it is the 10th anniversary of 9/11. Organizers of the Flags on the 48 tribute, which falls on a Sunday, are expecting a large turnout.

Hundreds have signed up to take part in the event this year, with all 48 peaks having at least some coverage. Registration is full on 25 peaks, with Boy Scout Troop 47 covering Tecumseh and Troop 91 bringing the flag up Wildcat “D”.

The plan is for the hikers to display the flag from noon to 2 p.m. After that, hikers will take the flags and accessories down the trail with them, abiding by the Leave No Trace outdoor ethics.

Three peaks are reserved for non-hikers: Washington, Cannon and Wildcat “D”, which have lifts or other transportation to their tops. Each peak has a coordinator who delegates who brings what and other details.

Registration for the 2011 event is still open, and you can sign up by going to www.flagsonthe48.org, or email contact@flagsonthe48.org.