A large American flag was unfurled at the Pentagon this morning to commemorate 9/11.

A little history: Here is why it is done:

At the Pentagon, the crash shook the building so hard that many inside wondered if there had been an earthquake. One hundred eight-four people were killed, ranging from Army Lt. Gen. Timothy J. Maude to rank-and-file service members and civilians working in the building.

As this Defense Department account recalls, the military unfurled a massive flag down the side of the building, just to the right of where the wreckage of the crash smoldered. Army Maj. Gen. Jim Jackson, commanding general at the time of the Military District of Washington, called for one at nearby Fort Myer, Va., and the U.S. Army Band sent a garrison flag — the largest authorized in the military, at about 20 feet by 38 feet.

The flag flew for one month, but the Pentagon has continued the tradition.

And a touching and moving tradition it is.

Chills and tears.

Amen. Never forget.