Once completed, the 8-acre memorial will form a tree-filled, cobblestoned plaza that surrounds twin reflecting pools built above the World Trade Center towers’ footprints.

Approximately 170 cubic yards (130 cubic meters) of concrete were poured near the reflecting pool being built over the north tower footprint forming the beginning of the street-level plaza in which the owners of the site hope to have opened by the 10th anniversary of the September 11 terrorist attacks.

This story originally appeared in Engineering News-Record.