Each of these 168 empty chairs represent a life lost on April 19, 1995, (the day that Timothy McVeigh bombed the Murrah Building in Oklahoma City); with smaller chairs representing the 19 children lost. These are arranged in nine rows, one for each of the nine floors of the building.
This memorial is quite impressive. I'll probably post at least a couple of more photos from the memorial over the next days.
I agree, most impressive and very moving. It is sort of like the Vietnam Memorial - you can't help be feel the loss and the senselessness of the act. Beautiful shot.