Each segment was 12 feet high, four feet wide and up to nine inches thick, according to “The Berlin Wall and the Intra-German Border, 1961-89,” by Gordon L. Rottman. Sewer piping crowned the wall so that there would be no edges for escapees to grasp.

When Mr. Speyer learned that an entrepreneur had arranged with the government to sell surviving segments, he and a business partner headed to a parking lot in which hundreds had been assembled, helter-skelter.

As if solving a giant jigsaw puzzle, the Tishman Speyer executives pieced together a contiguous five-segment section, with a huge yellow face that “really pops out at you,” Mr. Speyer said. (He paid about $50,000.) As it happens, this particular section can briefly be seen in the 1987 film “Wings of Desire.”

“I thought it was historically important,” Mr. Speyer said, “and some of the art was really pretty interesting.” Though he did not buy the section with 520 Madison Avenue in mind, the plaza there soon presented itself as an obvious setting.

But there was a problem. The wall stood in front of a waterfall.

Though several feet distant, the constant spray infiltrated the absorbent concrete, corroding the embedded steel rebar. As the moist concrete froze and thawed, expanding and contracting, it cracked and spalled. Paint started flaking off.