Four dozen flags will again be waving from atop New Hampshire's highest peaks in honor of the lives lost in the Sept. 11 terrorist attacks.

The 18th annual "Flags on the 48" memorial hike is being held Saturday, when participants will place American flags on the summit of each of the 48 mountains in New Hampshire with peaks above 4,000 feet.

Organizers say the first hike was a spontaneous effort by six hikers who raised a large flag on Mount Liberty on the first Saturday after the attacks in 2001.