It took three years, but Tobin managed to convince officials of the chapel's parent, Trinity Church, to allow him to restore the root and stump of that tree and to create from it castings for a sculpture to be placed next to the Trinity Church building at Broadway and Wall Street.

The result is The Trinity Root, a three-ton, 20-foot-long, rust-red sculpture painstakingly created from more than 300 bronze castings of the original (which has been returned to St. Paul's).

Last month, a crane lifted the artwork from a flatbed truck on Broadway, over the church's eight-foot-high fence, and into the church's courtyard.

For the artist, who has worked with root sculptures in the past, The Trinity Root is a potent symbol of the unity that sprang from the horror.

"When they knocked down our towers they really uncovered the strength of people across the U.S. and the world," Tobin said. "It brought us together. So my work is really meant to bring to light the unseen."

The rector of Trinity Church, the Rev. Dr. James Cooper, interprets the piece from a theological perspective. For Christians, he said, it can be a symbol of resurrection and new life. But there is something in the sculpture for all faiths and traditions, he added.

"You'll bring to it your own signs and symbols," Cooper said, "to wrestle with those basic issues of life, death and hope."