"Mr. Gorbachev . . .

If there's one thing that the myth of Ronald Reagan is built on, it's this speech.

Which should make the irony of this news even more painful.

Trying to stem the infiltration of militia fighters, American forces have begun to build a massive concrete wall that will partition Sadr City, the densely populated Shiite neighborhood in the Iraqi capital.

The construction, which began Tuesday night, is intended to turn the southern quarter of Sadr City near the international Green Zone into a protected enclave, secured by Iraqi and American forces, where the Iraqi government can undertake reconstruction efforts.

“You can’t really repair anything that is broken until you establish security,” said Lt. Col. Dan Barnett, commander of the First Squadron, Second Stryker Cavalry Regiment. “A wall that isolates those who would continue to attack the Iraqi Army and coalition forces can create security conditions that they can go in and rebuild.”

On Wednesday night, huge cranes slowly lifted heavy concrete blocks into place under a moonless sky. The barriers were implanted on Al Quds Street, a major thoroughfare that separates the Tharwa and Jamilla districts to the south from the heart of Sadr City to the north.

The avenue was quiet except for the whirring sound of the cranes and thud of the barriers as they touched the ground. Contractors operated the cranes, but American soldiers transported the barriers on trucks and directed their placement.

The team building the barrier was protected by M-1 tanks, Stryker vehicles and Apache attack helicopters. As the workers labored in silence, there was a burst of fire as an M-1 tank blasted its main gun at a small group of fighters to the west. An Apache helicopter fired a Hellfire missile at a militia team equipped with rocket-propelled grenades, again interrupting the night with a thunderous boom. A cloud of dark smoke was visible in the distance through the Stryker’s night-vision system.

Concrete barriers have been employed in other areas of Baghdad. As the barriers were being erected in other neighborhoods, some residents said they feared being isolated. But walls have often proved to be an effective tool in blunting insurgent attacks.

I'm trying to imagine the effect of, say, Ahmadinejad standing in Baghdad giving a speech that included the line: "Mr. President, Tear down this wall."

That would be pretty effective, dontcha think?